Production method of modified polytetrafluoroethylene and composition

ABSTRACT

A method for producing modified polytetrafluoroethylene including: polymerizing tetrafluoroethylene and a modifying monomer in an aqueous medium in the presence of a polymer (I) containing a polymerization unit (I) based on a monomer represented by the following general formula (I) to obtain a modified polytetrafluoroethylene:CX1X3═CX2R(—CZ1Z2-A0)m  (I)wherein X1 and X3 are each independently F, Cl, H, or CF3; X2 is H, F, an alkyl group, or a fluorine-containing alkyl group; A0 is an anionic group; R is a linking group; Z1 and Z2 are each independently H, F, an alkyl group, or a fluorine-containing alkyl group; and m is an integer of 1 or more. Also disclosed is a composition containing the modified polytetrafluoroethylene and the polymer (I).

TECHNICAL FIELD

The present disclosure relates to a method for producing modifiedpolytetrafluoroethylene and a composition.

BACKGROUND ART

Fluorinated anion surfactants have been used in production ofpolytetrafluoroethylene by emulsion polymerization.

Various methods for producing polytetrafluoroethylene are investigated,and for example, Patent Document 1 discloses a method for producing anaqueous dispersion containing rod-shaped fine particles ofpolytetrafluoroethylene having an average aspect ratio of 2 or more,wherein tetrafluoroethylene is polymerized in the presence of a polymercomposed of a polymerization unit represented by formula 1 or acopolymer composed of a polymerization unit represented by formula 1 anda polymerization unit represented by formula 2 (provided that thepolymerization unit represented by formula 1 accounts for 40 mol % ormore of all polymerization units):

provided that in formula 1, R^(f) is a perfluoroperfluoroalkylene grouphaving 1 to 6 carbon atoms, and M is an alkali metal ion or an ammoniumion, and in formula 2, X is a fluorine atom or a chlorine atom.

Patent Document 2 discloses particles comprising a bulk of afluoropolymer and a nucleus of a fluorinated ionomer. Patent Document 3discloses a method for making an aqueous dispersion of fluoropolymerparticles, comprising providing dispersed particulates of a fluorinatedionomer in an aqueous polymerization medium and polymerizing at leastone fluorinated monomer in the aqueous polymerization medium in thepresence of the dispersed particulates of a fluorinated ionomer and aninitiator to form the aqueous dispersion of fluoropolymer particles.

RELATED ART Patent Documents

-   Patent Document 1: Japanese Patent Laid-Open No. 11-181009-   Patent Document 2: Japanese Translation of PCT International    Application Publication No. 2012-513532-   Patent Document 3: Japanese Translation of PCT International    Application Publication No. 2012-513530

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The present disclosure provides a method for producing modifiedpolytetrafluoroethylene, from which an aqueous dispersion of particlesof modified polytetrafluoroethylene having a small average primaryparticle size can be obtained.

Means for Solving the Problem

The present disclosure relates to a method for producing modifiedpolytetrafluoroethylene comprising:

polymerizing tetrafluoroethylene and a modifying monomer in an aqueousmedium in the presence of a polymer (I) containing a polymerization unit(I) based on a monomer represented by the following general formula (I)to obtain a modified polytetrafluoroethylene:

CX¹X³═CX²R(—CZ¹Z²-A⁰)_(m)  (I)

wherein X¹ and X³ are each independently F, Cl, H, or CF₃; X² is H, F,an alkyl group, or a fluorine-containing alkyl group; A⁰ is an anionicgroup; R is a linking group; Z¹ and Z² are each independently H, F, analkyl group, or a fluorine-containing alkyl group; and m is an integerof 1 or more.

The production method of the present disclosure preferably furthercomprises adding the modifying monomer before the initiation ofpolymerization or when the concentration of particles of the modifiedpolytetrafluoroethylene formed in the aqueous medium is 5.0% by mass orless.

The total amount of the modifying monomer is preferably 0.00001% by massor more based on the obtained modified polytetrafluoroethylene. Further,the total amount of the modifying monomer is preferably 1.0% by mass orless based on the obtained modified polytetrafluoroethylene.

The modifying monomer preferably contains at least one selected from thegroup consisting of hexafluoropropylene, a perfluoro(alkyl vinyl ether),and a (perfluoroalkyl)ethylene.

The modifying monomer is also preferably a compound represented by thefollowing general formula (4):

CX^(i)X^(k)—CX^(j)R^(a)—(CZ¹Z²)_(k)—Y³  (4)

wherein X^(i), X^(j), and X^(k) are each independently F, Cl, H, or CF₃;Y³ is a hydrophilic group; R^(a) is a linking group; Z¹ and Z² are eachindependently H, F, or CF₃; and k is 0 or 1.

In the polymerization, tetrafluoroethylene and the modifying monomer maybe polymerized further in the presence of a nucleating agent. Thenucleating agent may be a nonionic surfactant.

The modified polytetrafluoroethylene preferably has an average primaryparticle size of 500 nm or less.

The modified polytetrafluoroethylene preferably has an aspect ratio ofprimary particles of less than 2.00.

The anionic group is preferably an anionic group that is a sulfategroup, a carboxylate group, a phosphate group, a phosphonate group, asulfonate group, or —C(CF₃)₂OM wherein M is —H, a metal atom, —NR⁷ ₄,imidazolium optionally having a substituent, pyridinium optionallyhaving a substituent, or phosphonium optionally having a substituent,and R⁷ is H or an organic group.

The present disclosure also relates to a composition comprising amodified polytetrafluoroethylene and a polymer (I) containing apolymerization unit (I) based on a monomer represented by the followinggeneral formula (I):

CX¹X³═CX²R(—CZ¹Z²-A⁰)_(m)  (I)

wherein X¹ and X³ are each independently F, Cl, H, or CF₃; X² is H, F,an alkyl group, or a fluorine-containing alkyl group; A⁰ is an anionicgroup; R is a linking group; Z¹ and Z² are each independently H, F, analkyl group, or a fluorine-containing alkyl group; and m is an integerof 1 or more.

The composition of the present disclosure preferably has a breakingstrength of 10.0 N or more.

The composition of the present disclosure preferably has a stressrelaxation time of 50 seconds or more.

The composition of the present disclosure preferably has an extrusionpressure of 10.0 MPa or more and 30.0 MPa or less.

The composition of the present disclosure preferably has an endothermicpeak temperature in the range of 333 to 347° C. The composition of thepresent disclosure preferably has a standard specific gravity of 2.250or less.

In the composition of the present disclosure, the modifiedpolytetrafluoroethylene preferably has an aspect ratio of primaryparticles of less than 2.00.

The anionic group is preferably an anionic group that is a sulfategroup, a carboxylate group, a phosphate group, a phosphonate group, asulfonate group, or —C(CF₃)₂OM wherein M is —H, a metal atom, —NR⁷ ₄,imidazolium optionally having a substituent, pyridinium optionallyhaving a substituent, or phosphonium optionally having a substituent,and R⁷ is H or an organic group.

The composition of the present disclosure is preferably substantiallyfree from a fluorine-containing surfactant.

The composition of the present disclosure is preferably a powder.

Effects of Invention

Having the above structure, the production method of the presentdisclosure is capable of providing an aqueous dispersion in which theaverage primary particle size of particles of modifiedpolytetrafluoroethylene is small.

DESCRIPTION OF EMBODIMENTS

Hereinafter, specific embodiments of the present disclosure will bedescribed in detail, but the present disclosure is not limited to thefollowing embodiments.

Before specifically describing the present disclosure, some terms usedherein are defined or explained.

The term “organic group” as used herein, unless otherwise specified,means a group containing one or more carbon atoms or a group obtainableby removing one hydrogen atom from an organic compound.

Examples of the “organic group” include:

an alkyl group optionally having one or more substituents,

an alkenyl group optionally having one or more substituents,

an alkynyl group optionally having one or more substituents,

a cycloalkyl group optionally having one or more substituents,

a cycloalkenyl group optionally having one or more substituents,

a cycloalkadienyl group optionally having one or more substituents,

an aryl group optionally having one or more substituents,

an aralkyl group optionally having one or more substituents,

a non-aromatic heterocyclic group optionally having one or moresubstituents,

a heteroaryl group optionally having one or more substituents,

a cyano group,

a formyl group,

RaO—,

RaCO—,

RaSO₂—,

RaCOO—,

RaNRaCO—,

RaCONRa—,

RaOCO—RaOSO₂—, and

RaNRbSO₂—,

wherein each Ra is independently

an alkyl group optionally having one or more substituents,

an alkenyl group optionally having one or more substituents,

an alkynyl group optionally having one or more substituents,

a cycloalkyl group optionally having one or more substituents,

a cycloalkenyl group optionally having one or more substituents,

a cycloalkadienyl group optionally having one or more substituents,

an aryl group optionally having one or more substituents,

an aralkyl group optionally having one or more substituents,

a non-aromatic heterocyclic group optionally having one or moresubstituents,

a heteroaryl group optionally having one or more substituents, and

Rb is independently H or an alkyl group optionally having one or moresubstituents.

The organic group is preferably an alkyl group optionally having one ormore substituents.

The term “substituent” as used herein, unless otherwise specified, meansa group capable of replacing another atom or group. Examples of the“substituent” include an aliphatic group, an aromatic group, aheterocyclic group, an acyl group, an acyloxy group, an acylamino group,an aliphatic oxy group, an aromatic oxy group, a heterocyclic oxy group,an aliphatic oxycarbonyl group, an aromatic oxycarbonyl group, aheterocyclic oxycarbonyl group, a carbamoyl group, an aliphatic sulfonylgroup, an aromatic sulfonyl group, a heterocyclic sulfonyl group, analiphatic sulfonyloxy group, an aromatic sulfonyloxy group, aheterocyclic sulfonyloxy group, a sulfamoyl group, an aliphaticsulfonamide group, an aromatic sulfonamide group, a heterocyclicsulfonamide group, an amino group, an aliphatic amino group, an aromaticamino group, a heterocyclic amino group, an aliphatic oxycarbonylaminogroup, an aromatic oxycarbonylamino group, a heterocyclicoxycarbonylamino group, an aliphatic sulfinyl group, an aromaticsulfinyl group, an aliphatic thio group, an aromatic thio group, ahydroxy group, a cyano group, a sulfo group, a carboxy group, analiphatic oxyamino group, an aromatic oxy amino group, a carbamoylaminogroup, a sulfamoylamino group, a halogen atom, a sulfamoylcarbamoylgroup, a carbamoyl sulfamoyl group, a dialiphatic oxyphosphinyl group,and a diaromatic oxyphosphinyl group.

The aliphatic group may be saturated or unsaturated, and may have ahydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphaticoxycarbonyl group, an aliphatic thio group, an amino group, an aliphaticamino group, an acylamino group, a carbamoylamino group, or the like.Examples of the aliphatic group include alkyl groups having 1 to 8,preferably 1 to 4 carbon atoms in total, such as a methyl group, anethyl group, a vinyl group, a cyclohexyl group, and a carbamoylmethylgroup.

The aromatic group may have, for example, a nitro group, a halogen atom,an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonylgroup, an aliphatic thio group, an amino group, an aliphatic aminogroup, an acylamino group, a carbamoylamino group, or the like. Examplesof the aromatic group include aryl groups having 6 to 12 carbon atoms,preferably 6 to 10 carbon atoms in total, such as a phenyl group, a4-nitrophenyl group, a 4-acetylaminophenyl group, and a4-methanesulfonylphenyl group.

The heterocyclic group may have a halogen atom, a hydroxy group, analiphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group,an aliphatic thio group, an amino group, an aliphatic amino group, anacylamino group, a carbamoylamino group, or the like. Examples of theheterocyclic group include 5- or 6-membered heterocyclic groups having 2to 12, preferably 2 to 10 carbon atoms in total, such as a2-tetrahydrofuryl group and a 2-pyrimidyl group.

The acyl group may have an aliphatic carbonyl group, an arylcarbonylgroup, a heterocyclic carbonyl group, a hydroxy group, a halogen atom,an aromatic group, an aliphatic oxy group, a carbamoyl group, analiphatic oxycarbonyl group, an aliphatic thio group, an amino group, analiphatic amino group, an acylamino group, a carbamoylamino group, orthe like. Examples of the acyl group include acyl groups having 2 to 8,preferably 2 to 4 carbon atoms in total, such as an acetyl group, apropanoyl group, a benzoyl group, and a 3-pyridinecarbonyl group.

The acylamino group may have an aliphatic group, an aromatic group, aheterocyclic group, or the like, and may have, for example, anacetylamino group, a benzoylamino group, a 2-pyridinecarbonylaminogroup, a propanoylamino group, or the like. Examples of the acylaminogroup include acylamino groups having 2 to 12, preferably 2 to 8 carbonatoms in total, and alkylcarbonylamino groups having 2 to 8 carbon atomsin total, such as an acetylamino group, a benzoylamino group, a2-pyridinecarbonylamino group, and a propanoylamino group.

The aliphatic oxycarbonyl group may be saturated or unsaturated, and mayhave a hydroxy group, an aliphatic oxy group, a carbamoyl group, analiphatic oxycarbonyl group, an aliphatic thio group, an amino group, analiphatic amino group, an acylamino group, a carbamoylamino group, orthe like. Examples of the aliphatic oxycarbonyl group includealkoxycarbonyl groups having 2 to 8, preferably 2 to 4 carbon atoms intotal, such as a methoxycarbonyl group, an ethoxycarbonyl group, and a(t)-butoxycarbonyl group.

The carbamoyl group may have an aliphatic group, an aromatic group, aheterocyclic group, or the like. Examples of the carbamoyl group includean unsubstituted carbamoyl group and alkylcarbamoyl groups having 2 to 9carbon atoms in total, preferably an unsubstituted carbamoyl group andalkylcarbamoyl groups having 2 to 5 carbon atoms in total, such as aN-methylcarbamoyl group, a N,N-dimethylcarbamoyl group, and aN-phenylcarbamoyl group.

The aliphatic sulfonyl group may be saturated or unsaturated, and mayhave a hydroxy group, an aromatic group, an aliphatic oxy group, acarbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thiogroup, an amino group, an aliphatic amino group, an acylamino group, acarbamoylamino group, or the like. Examples of the aliphatic sulfonylgroup include alkylsulfonyl groups having 1 to 6 carbon atoms in total,preferably 1 to 4 carbon atoms in total, such as a methanesulfonylgroup.

The aromatic sulfonyl group may have a hydroxy group, an aliphaticgroup, an aliphatic oxy group, a carbamoyl group, an aliphaticoxycarbonyl group, an aliphatic thio group, an amino group, an aliphaticamino group, an acylamino group, a carbamoylamino group, or the like.Examples of the aromatic sulfonyl group include arylsulfonyl groupshaving 6 to 10 carbon atoms in total, such as a benzenesulfonyl group.

The amino group may have an aliphatic group, an aromatic group, aheterocyclic group, or the like.

The acylamino group may have, for example, an acetylamino group, abenzoylamino group, a 2-pyridinecarbonylamino group, a propanoylaminogroup, or the like. Examples of the acylamino group include acylaminogroups having 2 to 12 carbon atoms in total, preferably 2 to 8 carbonatoms in total, and more preferably alkylcarbonylamino groups having 2to 8 carbon atoms in total, such as an acetylamino group, a benzoylaminogroup, a 2-pyridinecarbonylamino group, and a propanoylamino group.

The aliphatic sulfonamide group, aromatic sulfonamide group, andheterocyclic sulfonamide group may be, for example, a methanesulfonamidegroup, a benzenesulfonamide group, a 2-pyridinesulfonamide group,respectively.

The sulfamoyl group may have an aliphatic group, an aromatic group, aheterocyclic group, or the like. Examples of the sulfamoyl group includea sulfamoyl group, alkylsulfamoyl groups having 1 to 9 carbon atoms intotal, dialkylsulfamoyl groups having 2 to 10 carbon atoms in total,arylsulfamoyl groups having 7 to 13 carbon atoms in total, andheterocyclic sulfamoyl groups having 2 to 12 carbon atoms in total, morepreferably a sulfamoyl group, alkylsulfamoyl groups having 1 to 7 carbonatoms in total, dialkylsulfamoyl groups having 3 to 6 carbon atoms intotal, arylsulfamoyl groups having 6 to 11 carbon atoms in total, andheterocyclic sulfamoyl groups having 2 to 10 carbon atoms in total, suchas a sulfamoyl group, a methylsulfamoyl group, a N,N-dimethylsulfamoylgroup, a phenylsulfamoyl group, and a 4-pyridinesulfamoyl group.

The aliphatic oxy group may be saturated or unsaturated, and may have amethoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxygroup, a methoxyethoxy group, or the like. Examples of the aliphatic oxygroup include alkoxy groups having 1 to 8, preferably 1 to 6 carbonatoms in total, such as a methoxy group, an ethoxy group, an i-propyloxygroup, a cyclohexyloxy group, and a methoxyethoxy group.

The aromatic amino group and the heterocyclic amino group each may havean aliphatic group, an aliphatic oxy group, a halogen atom, a carbamoylgroup, a heterocyclic group ring-fused with the aryl group, and analiphatic oxycarbonyl group, preferably an aliphatic group having 1 to 4carbon atoms in total, an aliphatic oxy group having 1 to 4 carbon atomsin total, a halogen atom, a carbamoyl group having 1 to 4 carbon atomsin total, a nitro group, or an aliphatic oxycarbonyl group having 2 to 4carbon atoms in total.

The aliphatic thio group may be saturated or unsaturated, and examplesthereof include alkylthio groups having 1 to 8 carbon atoms in total,more preferably 1 to 6 carbon atoms in total, such as a methylthiogroup, an ethylthio group, a carbamoylmethylthio group, and at-butylthio group.

The carbamoylamino group may have an aliphatic group, an aryl group, aheterocyclic group or the like. Examples of the carbamoylamino groupinclude a carbamoylamino group, alkylcarbamoylamino groups having 2 to 9carbon atoms in total, dialkylcarbamoylamino groups having 3 to 10carbon atoms in total, arylcarbamoylamino groups having 7 to 13 carbonatoms in total, and heterocyclic carbamoylamino groups having 3 to 12carbon atoms in total, preferably a carbamoylamino group,alkylcarbamoylamino groups having 2 to 7 carbon atoms in total,dialkylcarbamoylamino groups having 3 to 6 carbon atoms in total,arylcarbamoylamino groups having 7 to 11 carbon atoms in total, andheterocyclic carbamoylamino groups having 3 to 10 carbon atoms in total,such as a carbamoylamino group, a methylcarbamoylamino group, aN,N-dimethylcarbamoylamino group, a phenylcarbamoylamino group, and a4-pyridinecarbamoylamino group.

The ranges expressed by the endpoints as used herein each include allnumerical values within the range (for example, the range of 1 to 10includes 1.4, 1.9, 2.33, 5.75, 9.98, and the like).

The phrase “at least one” as used herein includes all numerical valuesequal to or greater than 1 (for example, at least 2, at least 4, atleast 6, at least 8, at least 10, at least 25, at least 50, at least100, and the like).

Next, the production method of the present disclosure will now bespecifically described.

The method for producing modified polytetrafluoroethylene [modifiedPTFE] of the present disclosure includes the polymerization step ofpolymerizing tetrafluoroethylene [TFE] and a modifying monomer in anaqueous medium in the presence of a polymer (I) to obtain modified PTFE.The production method of the present disclosure is capable of producingmodified PTFE using the polymer (I) and also providing an aqueousdispersion in which the average primary particle size of particles ofmodified polytetrafluoroethylene is small. Further, an aqueousdispersion having a small aspect ratio and superior stability can beobtained.

The modified PTFE contains 99.0% by mass or more of a polymerizationunit based on TFE and 1.0% by mass or less of a polymerization unitbased on the modifying monomer.

In the modified PTFE, the content of the polymerization unit based onthe modifying monomer (hereinafter also referred to as a “modifyingmonomer unit”) is preferably in the range of 0.00001 to 1.0% by massbased on all polymerization units of PTFE. The lower limit of themodifying monomer is more preferably 0.0001% by mass, still morepreferably 0.001% by mass, further preferably 0.005% by mass, andparticularly preferably 0.009% by mass. The upper limit of the modifyingmonomer unit is 0.90% by mass, 0.50% by mass, 0.40% by mass, 0.30% bymass, 0.20% by mass, 0.15% by mass, 0.10% by mass, 0.08% by mass, 0.05%by mass, and 0.01% by mass in the order of preference. The term“modifying monomer unit” as used herein means a portion of the molecularstructure of the modified PTFE as a part derived from the modifyingmonomer.

In the present disclosure, the contents of the respective monomer unitsconstituting the modified PTFE can be calculated by any appropriatecombination of NMR, FT-IR, elemental analysis, X-ray fluorescenceanalysis, and other known methods in accordance with the types of themonomers. Further, the contents of the respective monomers constitutingPTFE can also be obtained by calculation from the amount of the addedmodifying monomer used in the polymerization.

The modifying monomer is not limited as long as it can be copolymerizedwith TFE, and examples thereof include fluoromonomers andnon-fluoromonomers. Further, a plurality of kinds of the modifyingmonomers may be used.

Examples of the non-fluoromonomer include, but not particularly to, amonomer represented by the general formula:

CH₂═CR^(Q1)-LR^(Q9)

(wherein R^(Q1) represents a hydrogen atom or an alkyl group; Lrepresents a single bond, —CO—O—*, —O—CO—*, or —O—; * represents thebinding position with R². R⁹² represents a hydrogen atom, an alkylgroup, or a nitrile group.

Examples of the non-fluoromonomer include methyl acrylate, methylmethacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate,propyl methacrylate butyl acrylate, butyl methacrylate, hexylmethacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinylacetate, acrylic acid, methacrylic acid, acrylonitrile,methacrylonitrile, ethyl vinyl ether, and cyclohexyl vinyl ether. Amongthese, the non-fluoromonomer is preferably butyl methacrylate, vinylacetate, or acrylic acid.

Examples of the fluoromonomer include perfluoroolefins such ashexafluoropropylene (HFP); hydrogen-containing fluoroolefins such astrifluoroethylene and vinylidene fluoride (VDF); perhaloolefins such aschlorotrifluoroethylene; perfluorovinyl ethers;(perfluoroalkyl)ethylenes; and perfluoroallyl ethers.

Examples of the perfluorovinyl ether include, but are not limited to, aperfluoro unsaturated compound represented by the following generalformula (A):

CF₂═CF—ORf  (A)

wherein Rf represents a perfluoroorganic group. The “perfluoroorganicgroup” as used herein means an organic group in which all hydrogen atomsbonded to the carbon atoms are replaced by fluorine atoms. Theperfluoroorganic group optionally has ether oxygen.

Examples of the perfluorovinyl ether include perfluoro(alkyl vinylether) (PAVE) in which Rf is a perfluoroalkyl group having 1 to 10carbon atoms in the general formula (A). The perfluoroalkyl grouppreferably has 1 to 5 carbon atoms.

Examples of the perfluoroalkyl group in PAVE include a perfluoromethylgroup, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutylgroup, a perfluoropentyl group, and a perfluorohexyl group.

Examples of the perfluorovinyl ether further include those representedby the general formula (A) in which Rf is a perfluoro (alkoxyalkyl)group having 4 to 9 carbon atoms; those in which Rf is a grouprepresented by the following formula:

wherein m represents 0 or an integer of 1 to 4; and those in which Rf isa group represented by the following formula:

wherein n is an integer of 1 to 4.

Examples of hydrogen-containing fluoroolefins include CH₂═CF₂, CFH═CH₂,CFH═CF₂, CF₂═CFCF₃, CH₂═CFCF₃, CH₂═CHCF₃, CHF═CHCF₃ (E-form), andCHF═CHCF₃ (Z-form).

Examples of the (perfluoroalkyl)ethylene (PFAE) include, but are notlimited to, (perfluorobutyl) ethylene (PFBE), and (perfluorohexyl)ethylene.

Examples of the perfluoroallyl ether include fluoromonomers representedby the general formula:

CF₂═CF—CF₂—ORf

wherein Rf represents a perfluoroorganic group.

Rf in the above general formula is the same as Rf in the general formula(A). Rf is preferably a perfluoroalkyl group having 1 to 10 carbon atomsor a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms.Perfluoroallyl ether is preferably at least one selected from the groupconsisting of CF₂═CF—CF₂—O—CF₃, CF₂═CF—CF₂—O—C₂F₅, CF₂═CF—CF₂—O—C₃F₇,and CF₂═CF—CF₂—O—C₄F₉, more preferably at least one selected from thegroup consisting of CF₂═CF—CF₂—O—C₂F₅, CF₂═CF—CF₂—O—C₃F₇, andCF₂═CF—CF₂—O—C₄F₉, and still more preferably CF₂═CF—CF₂—O—CF₂CF₂CF₃.

The modifying monomer is also preferably exemplified by a comonomer (3)having a monomer reactivity ratio of 0.1 to 8. The presence of thecomonomer (3) makes it possible to obtain modified PTFE particles havinga small particle size and aspect ratio, and to obtain an aqueousdispersion having high dispersion stability.

The monomer reactivity ratio in the copolymerization with TFE is a valueobtained by dividing a rate constant when the propagating radical reactswith TFE when the propagating radical is less than a repeating unitbased on TFE by a rate constant when the propagating radical reacts witha comonomer. The lower this value is, the more reactive the comonomer iswith TFE. The reactivity ratio can be calculated by copolymerizing theTFE and the comonomer, determining the compositional features in thepolymer formed immediately after initiation, and calculating thereactivity ratio by Fineman-Ross equation.

The copolymerization is performed using 3,600 g of deionized degassedwater, 1,000 mass ppm of anonium perfluorcoctanoate based on the water,and 100 g of paraffin wax contained in an autoclave made of stainlesssteel with an internal volume of 6.0 L at a pressure of 0.78 MPaG and atemperature of 70° C. A comonomer in an amount of 0.05 g, 0.1 g, 0.2 g,0.5 g, or 1.0 g is added to the reactor, and then 0.072 g of anoniumpersulfate (20 mass ppm based on the water) is added thereto. Tomaintain the polymerization pressure at 0.78 MPaG, TFE is continuouslyfed thereinto. When the charged amount of TFE reaches 1,000 g, stirringis stopped and the pressure is released until the pressure in thereactor decreases to the atmospheric pressure. After cooling, theparaffin wax is separated to obtain an aqueous dispersion containing theresulting polymer. The aqueous dispersion is stirred so that theresulting polymer coagulates, and the polymer is dried at 150° C. Thecomposition in the resulting polymer is calculated by appropriatecombination of NMR, FT-IR, elemental analysis, and X-ray fluorescenceanalysis depending on the types of the monomers.

The comonomer (3) having a monomer reactivity ratio of 0.1 to 8 ispreferably at least one selected from the group consisting of comonomersrepresented by the formulas (3a) to (3d):

CH₂═CH—Rf¹  (3a)

wherein Rf¹ is a perfluoroalkyl group having 1 to 10 carbon atoms;

CF₂═CF—O—Rf²  (3b)

wherein Rf² is a perfluoroalkyl group having 1 to 2 carbon atoms;

CF₂═CF—O—(CF₂)_(n)CF═CF₂  (3c)

wherein n is 1 or 2; and

wherein X³ and X⁴ are each F, Cl, or a methoxy group; and Y isrepresented by the formula Y1 or Y2;

in the formula Y2, Z and Z′ are each F or a fluorinated alkyl grouphaving 1 to 3 carbon atoms.

The content of the comonomer (3) unit is preferably in the range of0.00001 to 1.0% by mass based on all polymerization units of themodified PTFE. The lower limit thereof is more preferably 0.0001% bymass, more preferably 0.0005% by mass, still more preferably 0.001% bymass, further preferably 0.005% by mass, and particularly preferably0.009% by mass. The upper limit is 0.90% by mass, 0.50% by mass, 0.40%by mass, 0.30% by mass, 0.20% by mass, 0.15% by mass, 0.10% by mass,0.08% by mass, 0.05% by mass, and 0.01% by mass in the order ofpreference.

The modifying monomer is preferably at least one selected from the groupconsisting of hexafluoropropylene, chlorotrifluoroethylene, vinylidenefluoride, perfluoro (alkyl vinyl ether), (perfluoroalkyl)ethylene,ethylene, and modifying monomers having a functional group capable ofreacting by radical polymerization and a hydrophilic group, in view ofobtaining an aqueous dispersion of polytetrafluoroethylene particleshaving a small average primary particle size, a small aspect ratio, andexcellent stability.

From the viewpoint of reactivity with TFE, the modifying monomerpreferably contains at least one selected from the group consisting ofhexafluoropropylene, perfluoro(alkyl vinyl ether), and(perfluoroalkyl)ethylene.

The modifying monomer more preferably contains at least one selectedfrom the group consisting of hexafluoropropylene, perfluoro(methyl vinylether), perfluoro (propyl vinyl ether), (perfluorobutyl)ethylene,(perfluorohexyl)ethylene, and (perfluorooctyl)ethylene. The total amountof the hexafluoropropylene unit, the perfluoro(alkyl vinyl ether) unitand the (perfluoroalkyl)ethylene unit is preferably in the range of0.00001 to 1.0% by mass based on all polymerization units of themodified PTFE. The lower limit of the total amount is more preferably0.001% by mass, still more preferably 0.005% by mass, and particularlypreferably 0.009% by mass. The upper limit is 0.50% by mass, 0.40% bymass, 0.30% by mass, 0.20% by mass, 0.15% by mass, 0.10% by mass, 0.08%by mass, 0.05% by mass, and 0.01% by mass in the order of preference.

In the production method of the present disclosure, the modifyingmonomer may be a modifying monomer having a functional group capable ofreacting by radical polymerization and a hydrophilic group (hereinafter,referred to as “modifying monomer (A)”).

The presence of the modifying monomer (A) makes it possible to generatemore particles during polymerization and obtain primary particles havinga smaller primary particle size and aspect ratio, and the amount ofuncoagulated polymer can also be reduced.

Examples of the hydrophilic group in the modifying monomer (A) include—NH₂, —PO₃M, —OPO₃M, —SO₃M, —OSO₃M, and —COOM, wherein M represents H, ametal atom, NR⁷ ₄, imidazolium optionally having a substituent,pyridinium optionally having a substituent, or phosphonium optionallyhaving a substituent, wherein R⁷ is H or an organic group, and may bethe same or different, and any two thereof may be bonded to each otherto form a ring. Of these, the hydrophilic group is preferably —SO₃M or—COOM. The alkyl group is preferable as the organic group in R^(7y). R⁷is preferably H or an organic group having 1 to 10 carbon atoms, morepreferably H or an organic group having 1 to 4 carbon atoms, and stillmore preferably H or an alkyl group having 1 to 4 carbon atoms.

Examples of the metal atom include monovalent and divalent metal atoms,alkali metals (Group 1) and alkaline earth metals (Group 2), andpreferred is Na, K, or Li.

Examples of the “functional group capable of reacting by radicalpolymerization” in the modifying monomer (A) include a group having anethylenically unsaturated bond such as a vinyl group and an allyl group.

The group having an ethylenically unsaturated bond may be represented bythe following formula:

CX^(e)X^(g)—CX^(f)R—

wherein X^(e), X^(f) and X^(g) are each independently F, Cl, H, CF₃,CF₂H, CFH₂ or CH₃; and R is a linking group. The linking group R includelinking groups as R^(a) which will be described later. Preferred aregroups having an unsaturated bond, such as —CH═CH₂, —CF═CH₂, —CH═CF₂,—CF═CF₂, —CH₂—CH═CH₂, —CF₂—CF═CH₂, —CF₂—CF═CF₂, —(C═O)—CH═CH₂,—(C═O)—CF═CH₂, —(C═O)—CH═CF₂, —(C═O)—CF═CF₂, —(C═O)—C(CH₃)═CH₂,—(C═O)—C(CF₃)═CH₂, —(C═O)—C(CH₃)═CF₂, —(C═O)—C(CF₃)═CF₂, —O—CH₂—CH═CH₂,—O—CF₂—CF═CH₂, —O—CH₂—CH═CF₂, and —O—CF₂—CF═CF₂.

Since the modifying monomer (A) has a functional group capable ofreacting by radical polymerization, it is presumed that when used in thepolymerization, it reacts with a fluorine-containing monomer at theinitial stage of the polymerization reaction and forms particles withhigh stability having a hydrophilic group derived from the modifyingmonomer (A). Therefore, it is considered that the number of particlesincreases when the polymerization is performed in the presence of themodifying monomer (A).

The polymerization may be performed in the presence of one or more ofthe modifying monomers (A).

In the polymerization, a compound having an unsaturated bond may be usedas the modifying monomer (A).

The modifying monomer (A) is preferably a compound represented by thegeneral formula (4):

CX^(i)X^(k)═CX^(j)R^(a)—(CZ¹Z²)_(k)—Y³  (4)

wherein X^(i), X^(j), and X^(k) are each independently F, Cl, H, or CF₃;Y³ is a hydrophilic group; R^(a) is a linking group; Z¹ and Z² are eachindependently H, F, or CF₃; and k is 0 or 1.

Examples of the hydrophilic group include —NH₂, —PO₃M, —OPO₃M, —SO₃M,—OSO₃M, and —COOM, wherein M represents H, a metal atom, NR^(7y) ₄,imidazolium optionally having a substituent, pyridinium optionallyhaving a substituent, or phosphonium optionally having a substituent,wherein R^(7y) is H or an organic group, and may be the same ordifferent, and any two thereof may be bonded to each other to form aring. Of these, the hydrophilic group is preferably —SO₃M or —COOM. Thealkyl group is preferable as the organic group in R^(7y). R^(7y) ispreferably H or a C₁₋₁₀ organic group, more preferably H or a C₁₋₄organic group, and still more preferably H or a C₁₋₄ alkyl group.

Examples of the metal atom include monovalent and divalent metal atoms,alkali metals (Group 1) and alkaline earth metals (Group 2), andpreferred is Na, K, or Li.

The use of the modifying monomer (A) allows for obtaining an aqueousdispersion having a smaller average primary particle size and superiorstability. Also, the aspect ratio of the primary particles can be madesmaller.

R^(a) is a linking group. The “linking group” as used herein refers to adivalent linking group. The linking group may be a single bond andpreferably contains at least one carbon atom, and the number of carbonatoms may be 2 or more, 4 or more, 8 or more, 10 or more, or 20 or more.The upper limit thereof is not limited, but may be 100 or less, and maybe 50 or less, for example.

The linking group may be linear or branched, cyclic or acyclic,saturated or unsaturated, substituted or unsubstituted, and optionallycontains one or more heteroatoms selected from the group consisting ofsulfur, oxygen, and nitrogen, and optionally contains one or morefunctional groups selected from the group consisting of esters, amides,sulfonamides, carbonyls, carbonates, urethanes, ureas and carbamates.The linking group may be free from carbon atoms and may be a catenaryheteroatom such as oxygen, sulfur, or nitrogen.

R^(a) is preferably a catenary heteroatom such as oxygen, sulfur, ornitrogen, or a divalent organic group.

When R^(a) is a divalent organic group, the hydrogen atom bonded to thecarbon atom may be replaced by a halogen other than fluorine, such aschlorine, and may or may not contain a double bond. Further, R^(a) maybe linear or branched, and may be cyclic or acyclic. R^(a) may alsocontain a functional group (e.g., ester, ether, ketone, amine, halide,etc.).

R^(a) may also be a fluorine-free divalent organic group or a partiallyfluorinated or perfluorinated divalent organic group.

R^(a) may be, for example, a hydrocarbon group in which a fluorine atomis not bonded to a carbon atom, a hydrocarbon group in which some of thehydrogen atoms bonded to a carbon atom are replaced by fluorine atoms, ahydrocarbon group in which all of the hydrogen atoms bonded to thecarbon atoms are replaced by fluorine atoms, —(C═O)—, —(C═O)—O—, or ahydrocarbon group containing —(C═O)—, and these groups optionallycontain an oxygen atom, optionally contain a double bond, and optionallycontain a functional group.

R^(a) is preferably —(C═O)—, —(C═O)—O—, or a hydrocarbon group having 1to 100 carbon atoms that optionally contains an ether bond andoptionally contains a carbonyl group, wherein some or all of thehydrogen atoms bonded to the carbon atoms in the hydrocarbon group maybe replaced by fluorine.

R^(a) is preferably at least one selected from —(CH₂)_(a)—, —(CF₂)_(a)—,—O—(CF₂)_(a)—, —(CF₂)_(a)—O—(CF₂)_(b)—, —O(CF₂)_(a)—O—(CF₂)_(b)—,—(CF₂)_(a)—[O—(CF₂)_(b)]_(c)—, —O(CF₂)_(a)—[O—(CF₂)_(b)]_(c)—,—[(CF₂)_(a)—O]_(b)—[(CF₂)_(c)—O]_(d)—,—O[(CF₂)_(a)—O]_(b)—[(CF₂)_(c)—O]_(d)—, —O—[CF₂CF(CF₃)O]_(a)—(CF₂)_(b)—,—(C═O)—, —(C═O)—O—, —(C═O)—(CH₂)_(a)—, —(C═O)—(CF₂)_(a)—,—(C═O)—O—(CH₂)_(a)—, —(C═O)—O—(CF₂)_(a)—, —(C═O)—[(CH₂)_(a)—O]_(b)—,—(C═O)—[(CF₂)_(a)—O]_(b)—, —(C═O)—O[(CH₂)_(a)—O]_(b)—,—(C═O)—O[(CF₂)_(a)—O]_(b)—, —(C═O)—O[(CH₂)_(a)—O]_(b)—(CH₂)_(c)—,—(C═O)—O[(CF₂)_(a)—O]_(b)—(CF₂)_(c)—, —(C═O)—(CH₂)_(a)—O—(CH₂)_(b)—,—(C═O)—(CF₂)_(a)—O—(CF₂)_(b)—, —(C═O)—O—(CH₂)_(a)—O—(CH₂)_(b)—,—(C═O)—O—(CF₂)_(a)—O—(CF₂)_(b)—, —(C═O)—O—C₆H₄—, and combinationsthereof.

In the formula, a, b, c, and d are independently at least 1 or more. a,b, c, and d may independently be 2 or more, 3 or more, 4 or more, 10 ormore, or 20 or more. The upper limits of a, b, c, and d are 100, forexample.

Specific examples suitable for R^(a) include —CF₂—O—, —CF₂—O—CF₂—,—CF₂—O—CH₂—, —CF₂—O—CH₂CF₂—, —CF₂—O—CF₂CF₂—, —CF₂—O—CF₂CH₂—,—CF₂—O—CF₂CF₂CH₂—, —CF₂—O—CF(CF₃)—, —CF₂—O—CF(CF₃)CF₂—,—CF₂—O—CF(CF₃)CF₂—O—, —CF₂—O—CF(CF₃)CH₂—, —(C═O)—, —(C═O)—O—,—(C═O)—(CH₂)—, —(C═O)—(CF₂)—, —(C═O)—O—(CH₂)—, —(C═O)—O—(CF₂)—,—(C═O)—[(CH₂)₂—O]_(n)—, —(C═O)—[(CF₂)₂—O]_(n)—, —(C═O)—O[(CH₂)₂—O]_(n)—,—(C═O)—O[(CF₂)₂—O]_(n)—, —(C═O)—O[(CH₂)₂—O]_(n)—(CH₂)—,—(C═O)—O[(CF₂)₂—O]_(n)—(CF₂)—, —(C═O)—(CH₂)₂—O—(CH₂)—,—(C═O)—(CF₂)₂—O—(CF₂)—, —(C═O)—O—(CH₂)₂—O—(CH₂)—,—(C═O)—O—(CF₂)₂—O—(CF₂)—, and —(C═O)—O—C₆H₄—. In particular, preferredfor R^(a) among these is —CF₂—O—, —CF₂—O—CF₂—, —CF₂—O—CF₂CF₂—,—CF₂—O—CF(CF₃)—, —CF₂—O—CF(CF₃)CF₂—, —CF₂—O—CF(CF₃)CF₂—O—, —(C═O)—,—(C═O)—O—, —(C═O)—(CH₂)—, —(C═O)—O—(CH₂)—, —(C═O)—O[(CH₂)₂—O]_(n)—,—(C═O)—O[(CH₂)₂—O]_(n)—(CH₂)—, —(C═O)—(CH₂)₂—O—(CH₂)—, or—(C═O)—O—C₆H₄—.

In the formula, n is an integer of 1 to 10.

—R^(a)—(CZ¹Z²)_(k)— in the general formula (4) is preferably—CF₂—O—CF₂—, —CF₂—O—CF(CF₃)—, —CF₂—O—C(CF₃)₂—, —CF₂—O—CF₂—CF₂—,—CF₂—O—CF₂—CF(CF₃)—, —CF₂—O—CF₂—C(CF₃)₂—, —CF₂—O—CF₂CF₂—CF₂—,—CF₂—O—CF₂CF₂—CF(CF₃)—, —CF₂—O—CF₂CF₂—C(CF₃)₂—, —CF₂—O—CF(CF₃)—CF₂—,—CF₂—O—CF(CF₃)—CF(CF₃)—, —CF₂—O—CF(CF₃)—C(CF₃)₂—, —CF₂—O—CF(CF₃)—CF₂—,—CF₂—O—CF(CF₃)—CF(CF₃)—, —CF₂—O—CF(CF₃)—C(CF₃)₂—,—CF₂—O—CF(CF₃)CF₂—CF₂—, —CF₂—O—CF(CF₃)CF₂—CF(CF₃)—,—CF₂—O—CF(CF₃)CF₂—C(CF₃)₂—, —CF₂—O—CF(CF₃)CF₂—O—CF₂—,—CF₂—O—CF(CF₃)CF₂—O—CF(CF₃)—, —CF₂—O—CF(CF₃)CF₂—O—C(CF₃)₂—, —(C═O)—,—(C═O)—O—, —(C═O)—(CH₂)—, —(C═O)—(CF₂)—, —(C═O)—O—(CH₂)—,—(C═O)—O—(CF₂)—, —(C═O)—[(CH₂)₂—O]_(n)—(CH₂)—,—(C═O)—[(CF₂)₂—O]_(n)—(CF₂)—, —(C═O)—[(CH₂)₂—O]_(n)—(CH₂)—(CH₂)—,—(C═O)—[(CF₂)₂—O]_(n)—(CF₂)—(CF₂)—, —(C═O)—O[(CH₂)₂—O]_(n)—(CF₂)—,—(C═O)—O[(CH₂)₂—O]_(n)—(CH₂)—(CH₂)—, —(C═O)—O[(CF₂)₂—O]_(n)—(CF₂)—,—(C═O)—O[(CF₂)₂—O]_(n)—(CF₂)—(CF₂)—, —(C═O)—(CH₂)₂—O—(CH₂)—(CH₂)—,—(C═O)—(CF₂)₂—O—(CF₂)—(CF₂)—, —(C═O)—O—(CH₂)₂—O—(CH₂)—(CH₂)—,—(C═O)—O—(CF₂)₂—O—(CF₂)—(CF₂)—, —(C═O)—O—(CH₂)₂—O—(CH₂)—C(CF₃)₂—,—(C═O)—O—(CF₂)₂—O—(CF₂)—C(CF₃)₂—, or —(C═O)—O—C₆H₄—C(CF₃)₂—, and is morepreferably —CF₂—O—CF(CF₃)—, —CF₂—O—CF₂—CF(CF₃)—, —CF₂—O—CF₂CF₂—CF(CF₃)—,—CF₂—O—CF(CF₃)—CF(CF₃)—, —CF₂—O—CF(CF₃)CF₂—CF(CF₃)—,—CF₂—O—CF(CF₃)CF₂—O—CF(CF₃)—, —(C═O)—, —(C═O)—O—(CH₂)—,—(C═O)—O—(CH₂)—(CH₂)—, —(C═O)—O[(CH₂)₂—O]_(n)—(CH₂)—(CH₂)—,—(C═O)—O—(CH₂)₂—O—(CH₂)—C(CF₃)₂—, or —(C═O)—O—C₆H₄—C(CF₃)₂—.

In the formula, n is an integer of 1 to 10.

Specific examples of the compound represented by the general formula (4)include compounds represented by the following formulas:

wherein X^(j) and Y³ are as described above; and n is an integer of 1 to10.

R^(a) is preferably a divalent group represented by the followinggeneral formula (r1):

(C═O)_(h)—(O)_(i)—CF₂—O—(CX⁶ ₂)_(e)—{O—CF(CF₃)}_(f)—(O)_(g)—  (r1)

wherein X⁶ is each independently H, F, or CF₃; e is an integer of 0 to3; f is an integer of 0 to 3; g is 0 or 1; h is 0 or 1; and i is 0 or 1,

and is also preferably a divalent group represented by the followinggeneral formula (r2):

(C═O)_(h)—(O)_(i)—CF₂—O—(CX⁷ ₂)_(e)—(O)_(g)—  (r2)

wherein X⁷ is each independently H, F, or CF₃; e is an integer of 0 to3; g is 0 or 1; h is 0 or 1; and i is 0 or 1.

—R^(a)—(CZ¹Z²)_(k)— in the general formula (4) is also preferably adivalent group represented by the following formula (t1):

(C═O)_(h)—(O)_(i)—CF₂—O—(CX⁶ ₂)_(e)—{O—CF(CF₃)}_(f)—(O)_(g)—CZ¹Z²—  (t1)

wherein X⁶ is each independently H, F, or CF₃; e is an integer of 0 to3; f is an integer of 0 to 3; g is 0 or 1; h is 0 or 1; i is 0 or 1; andZ¹ and Z² are each independently F or CF₃,

and is more preferably a group in which one of Z¹ and Z² is F and theother is CF₃ in the formula (t1).

Also, in the general formula (4), —R^(a)—(CZ¹Z²)_(k)— is preferably adivalent group represented by the following formula (t2):

(C═O)_(h)—(O)_(i)—CF₂—O—(CX⁷ ₂)_(e)—(O)_(g)—CZ¹Z²—  (t2)

wherein X⁷ is each independently H, F, or CF₃; e is an integer of 0 to3; g is 0 or 1; h is 0 or 1; i is 0 or 1; and Z¹ and Z² are eachindependently F or CF₃, and is more preferably a group in which one ofZ¹ and Z² is F and the other is CF₃ in the formula (t2).

The compound represented by the general formula (4) also preferably hasa C—F bond and does not have a C—H bond, in the portion excluding thehydrophilic group (Y³). In other words, in the general formula (4),X^(i), X^(j), and X^(k) are all F, and R^(a) is preferably aperfluoroalkylene group having 1 or more carbon atoms; theperfluoroalkylene group may be either linear or branched, may be eithercyclic or acyclic, and may contain at least one catenary heteroatom. Theperfluoroalkylene group may have 2 to 20 carbon atoms or 4 to 18 carbonatoms.

The compound represented by the general formula (4) may be partiallyfluorinated. In other words, the compound represented by the generalformula (4) also preferably has at least one hydrogen atom bonded to acarbon atom and at least one fluorine atom bonded to a carbon atom, inthe portion excluding the hydrophilic group (Y3).

The compound represented by the general formula (4) is also preferably acompound represented by the following formula (4a):

CF₂═CF—O—Rf⁰—Y³  (4a)

wherein Y³ is a hydrophilic group; and Rf⁰ is a perfluorinated divalentlinking group which is perfluorinated and may be a linear or branched,cyclic or acyclic, saturated or unsaturated, substituted orunsubstituted, and optionally contains one or more heteroatoms selectedfrom the group consisting of sulfur, oxygen, and nitrogen.

The compound represented by the general formula (4) is also preferably acompound represented by the following formula (4b):

CH₂═CH—O—Rf⁰—Y³  (4b)

wherein Y³ is a hydrophilic group; and Rf⁰ is a perfluorinated divalentlinking group as defined in the formula (4a).

In the general formula (4), Y³ is preferably —OSO₃M. Examples of thecompound represented by the general formula (4) when Y³ is —OSO₃Minclude CF₂═CF(OCF₂CF₂CH₂OSO₃M), CH₂═CH((CF₂)₄CH₂OSO₃M),CF₂═CF(O(CF₂)₄CH₂OSO₃M), CF₂═CF(OCF₂CF(CF₃)CH₂OSO₃M),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂CH₂OSO₃M), CH₂═CH((CF₂)₄CH₂OSO₃M),CF₂═CF(OCF₂CF₂SO₂N(CH₃)CH₂CH₂OSO₃M), CH₂═CH(CF₂CF₂CH₂OSO₃M),CF₂═CF(OCF₂)CF₂CF₂CF₂SO₂N(CH₃)CH₂CH₂OSO₃M), and CH₂═CH(CF₂CF₂CH₂OSO₃M).In the formulas, M is the same as above.

In a preferred embodiment, in the general formula (4), Y³ is —SO₃M.Examples of the compound represented by the general formula (4) when Y³is —SO₃M include CF₂═CF(OCF₂CF₂SO₃M), CF₂═CF(O(CF₂)₄SO₃M),CF₂═CF(OCF₂CF(CF₃) SO₃M), CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂SO₃M),CH₂═CH(CF₂CF₂SO₃M), CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂CF₂CF₂SO₃M),CH₂═CH((CF₂)₄SO₃M), CH₂═CH(CF₂CF₂SO₃M), and CH₂═CH((CF₂)₃SO₃M). In theformulas, M is the same as above.

In a preferred embodiment, in the general formula (4), Y³ is —COOM.Examples of the polymerization units derived from the compoundrepresented by the general formula (4) when Y³ is —COM includeCF₂═CF(OCF₂CF₂COOM), CF₂═CF(OCF₂CF₂CF₂COOM), CF₂═CF(O(CF₂)₅COOM),CF₂═CF(OCF₂CF(CF₃)COOM), CF₂═CF(OCF₂CF(CF₃)O(CF₂)_(n)COOM) (n is greaterthan 1), CH₂═CH(CF₂CF₂COOM), CH₂═CH((CF₂)₄COOM), CH₂═CH(CF₂CF₂COOM),CH₂═CH((CF₂)₃COOM), CF₂═CF(OCF₂CF₂SO₂NR′CH₂COOM),CF₂═CF(O(CF₂)₄SO₂NR′CH₂COOM), CF₂═CF(OCF₂CF(CF₃) SO₂NR′CH₂COOM),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂SO₂NR′CH₂COOM), CH₂═CH(CF₂CF₂SO₂NR CH₂COOM),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂CF₂CF₂SO₂NR′CH₂COOM),CH₂═CH((CF₂)₄SO₂NR′CH₂COOM), CH₂═CH(CF₂CF₂SO₂NR′CH₂COOM), andCH₂═CH(CF₂)(₄SO₂NR′CH₂COOM). In the formula, R′ is an H or C₁₋₄ alkylgroup, and M is the same as above.

In a preferred embodiment, in the general formula (4), Y³ is preferably—PO₃M or —OP(O)(OM)₂. Examples of the compound represented by thegeneral formula (4) when Y³ is —PO₃M or —OP(O)(OM)₂ includeCF₂═CF(OCF₂CF₂CH₂OP(O)(OM)₂), CF₂═CF(O(CF₂)₄CH₂OP(O)(CM)₂),CF₂═CF(OCF₂CF(CF₃)CH₂OP(O)(OM)₂),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂CH₂OP(O)(OM)₂),CF₂═CF(OCF₂CF₂SO₂N(CH₃)CH₂CH₂OP(O)(OM)₂),CF₂═CF(OCF₂CF₂CF₂CF₂SO₂N(CH₃)CH₂CH₂OP(O)(OM)₂),CH₂═CH(CF₂CF₂CH₂OP(O)(CM)₂), CH₂═CH((CF₂)₄CH₂OP(O)(OM)₂),CH₂═CH(CF₂CF₂CH₂OP(O)(CM)₂), and CH₂═CH((CF₂)₄CH₂OP(O)(OM)₂), wherein Mis as described above.

In a preferred embodiment, in the general formula (4), Y³ is preferably—PO₃M or —P(O)(OM)₂. Examples of the compound represented by the generalformula (4) when Y³ is —PO₃M or —P(O)(CM)₂ includeCF₂═CF(OCF₂CF₂P(O)(OM)₂), CF₂═CF(O(CF₂)₄P(O)(OM)₂), CF₂═CF(OCF₂CF(CF₃)P(O)(OM)₂), CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂P(O)(CM)₂),CH₂═CH(CF₂CF₂P(O)(CM)₂), CH₂═CH((CF₂)₄P(O)(CM)₂),CH₂═CH(CF₂CF₂P(O)(CM)₂), and CH₂═CH((CF₂)₄P(O)(CM)₂), wherein M is asdescribed above.

The compound represented by the general formula (4) is preferably atleast one selected from the group consisting of:

a monomer represented by the following general formula (5):

CX₂═CY(—CZ₂—O—Rf—Y³)  (5)

wherein X is the same or different and is —H or —F; Y is —H, —F, analkyl group, or a fluorine-containing alkyl group; Z is the same ordifferent and —H, —F, an alkyl group, or a fluorine-containing alkylgroup; Rf is a fluorine-containing alkylene group having 1 to 40 carbonatoms or a fluorine-containing alkylene group having 2 to 100 carbonatoms and having an ether bond; and Y³ is as described above;

a monomer represented by the following general formula (6):

CX₂═CY(—O—Rf—Y³)  (6)

wherein X is the same or different and is —H or —F; Y is —H, —F, analkyl group, or a fluorine-containing alkyl group; Rf is afluorine-containing alkylene group having 1 to 40 carbon atoms or afluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond; and Y³ is as described above; and

a monomer represented by the following general formula (7):

CX₂═CY(—Rf—Y³)  (7)

wherein X is the same or different and is —H or —F; Y is —H, —F, analkyl group, or a fluorine-containing alkyl group; Rf is afluorine-containing alkylene group having 1 to 40 carbon atoms or afluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond; and Y³ is as described above.

The fluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond is an alkylene group which does not include astructure in which an oxygen atom is an end and contains an ether bondbetween carbon atoms.

In the general formula (5), each X is H or F. Both X may be H, both maybe F, or at least one may be H. For example, one thereof may be F andthe other may be H, or both may be H.

In the general formula (5), Y is H, F, an alkyl group, or afluorine-containing alkyl group.

The alkyl group is an alkyl group free from fluorine atoms and may haveone or more carbon atoms. The alkyl group preferably has 6 or lesscarbon atoms, more preferably 4 or less carbon atoms, and still morepreferably 3 or less carbon atoms.

The fluorine-containing alkyl group is an alkyl group containing atleast one fluorine atom, and may have one or more carbon atoms. Thefluorine-containing alkyl group preferably has 6 or less carbon atoms,more preferably 4 or less carbon atoms, and still more preferably 3 orless carbon atoms.

Y is preferably —H, —F, or —CF₃, and more preferably —F.

In the general formula (5), Z is the same or different and is H, F, analkyl group, or a fluoroalkyl group.

The alkyl group is an alkyl group free from fluorine atoms and may haveone or more carbon atoms. The alkyl group preferably has 6 or lesscarbon atoms, more preferably 4 or less carbon atoms, and still morepreferably 3 or less carbon atoms.

The fluorine-containing alkyl group is an alkyl group containing atleast one fluorine atom, and may have one or more carbon atoms. Thefluorine-containing alkyl group preferably has 6 or less carbon atoms,more preferably 4 or less carbon atoms, and still more preferably 3 orless carbon atoms.

Z is preferably H, F, or CF₃, and more preferably F.

In the general formula (5), at least one of X, Y, and Z preferablycontains a fluorine atom. For example, X, Y, and Z may be H, F, and F,respectively.

In the general formula (5), Rf is a fluorine-containing alkylene grouphaving 1 to 40 carbon atoms or a fluorine-containing alkylene grouphaving 2 to 100 carbon atoms and having an ether bond. Thefluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond is an alkylene group which does not include astructure wherein an oxygen atom is an end and which contains an etherbond between carbon atoms.

The fluorine-containing alkylene group preferably has 2 or more carbonatoms. The fluorine-containing alkylene group also preferably has 30 orless carbon atoms, more preferably 20 or less carbon atoms, and stillmore preferably 10 or less carbon atoms. Examples of thefluorine-containing alkylene group include —CF₂—, —CH₂CF₂—, —CF₂CF₂—,—CF₂CH₂—, —CF₂CF₂CH₂—, —CF(CF₃)—, —CF(CF₃)CF₂—, and —CF(CF₃)CH₂—. Thefluorine-containing alkylene group is preferably a perfluoroalkylenegroup.

The fluorine-containing alkylene group having an ether bond preferablyhas 3 or more carbon atoms. Further, the fluorine-containing alkylenegroup having an ether bond preferably has 60 or less, more preferably 30or less, and still more preferably 12 or less carbon atoms. Thefluorine-containing alkylene group having an ether bond is alsopreferably a divalent group represented by the following formula:

(wherein Z¹ is F or CF₃; Z² and Z³ are each H or F; Z 4 is H, F, or CF₃;p1+q1+r1 is an integer of 0 to 10; s1 is 0 or 1; and t1 is an integer of0 to 5).

Specific examples of the fluorine-containing alkylene group having anether bond include —CF(CF₃)CF₂—O—CF(CF₃)—, —(CF(CF₃)CF₂—O)_(n)—CF(CF₃)—(where n is an integer of 1 to 10), —CF(CF₃)CF₂—O—CF(CF₃)CH₂—,—(CF(CF₃)CF₂—O)_(n)—CF(CF₃)CH₂— (where n is an integer of 1 to 10),—CH₂CF₂CF₂O—CH₂CF₂CH₂—, —CF₂CF₂CF₂O—CF₂CF₂—, —CF₂CF₂CF₂O—CF₂CF₂CH₂—,—CF₂CF₂O—CF₂—, and —CF₂CF₂O—CF₂CH₂—. The fluorine-containing alkylenegroup having an ether bond is preferably a perfluoroalkylene group.

In the general formula (5), Y³ is —COOM, —SO₃M, or —OSO₃M, wherein M isH, a metal atom, NR^(7y) ₄, imidazolium optionally having a substituent,pyridinium optionally having a substituent, or phosphonium optionallyhaving a substituent, wherein R^(7y) is H or an organic group, and maybe the same or different, and any two thereof may be bonded to eachother to form a ring.

The alkyl group is preferable as the organic group in R^(7y).

R^(7y) is preferably H or a C₁₋₁₀ organic group, more preferably H or aC₁₋₄ organic group, and still more preferably H or a C₁₋₄ alkyl group.

Examples of the metal atom include alkali metals (Group 1) and alkalineearth metals (Group 2), and preferred is Na, K, or Li.

M is preferably —H, a metal atom, or —NR^(7y) ₄, more preferably —H, analkali metal (Group 1), an alkaline earth metal (Group 2), or —NR^(7y)₄, still more preferably —H, —Na, —K, —Li, or —NH₄, further preferably—Na, —K, or —NH₄, particularly preferably —Na or —NH₄, and mostpreferably —NH₄.

Y³ is preferably —COOM or —SO₃M, and more preferably —COOM.

The monomer represented by the general formula (5a) is preferably amonomer (5a) represented by the following general formula (5a):

CH₂═CF(—CF₂—O—Rf—Y³)  (5a)

wherein Rf and Y³ are as described above.

Specific examples of the monomer represented by the general formula (5a)include a monomer represented by the following formula:

wherein Z¹ is F or CF₃; Z² and Z³ are each H or F; Z⁴ is H, F, or CF₃;p1+q1+r1 is an integer of 0 to 10; s1 is 0 or 1; t1 is an integer of 0to 5; and Y³ is as described above, with the proviso that when Z³ and Z⁴are both H, p1+q1+r1+s1 is not 0. More specifically, preferred examplesthereof include:

Of these, preferred are:

In the monomer represented by the general formula (5a), Y³ in theformula (5a) is preferably —COOM. Specifically, the monomer representedby the general formula (5a) is preferably at least one selected from thegroup consisting of CH₂═CFCF₂OCF(CF₃)COOM andCH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)COOM (wherein M is as defined above), andmore preferably CH₂═CFCF₂OCF(CF₃)COOM.

The monomer represented by the general formula (5b) is preferably amonomer (5b) represented by the following general formula (5b):

CX² ₂═CFCF₂—O—(CF(CF₃)CF₂O)_(n5)—CF(CF₃)—Y³  (5b)

wherein each X² is the same, and each represent F or H; n5 represents 0or an integer of 1 to 10, and Y³ is as defined above.

In the formula (5b), n5 is preferably 0 or an integer of 1 to 5, morepreferably 0, 1, or 2, and still more preferably 0 or 1 from theviewpoint of stability of the resulting aqueous dispersion. Y³ ispreferably —COOM from the viewpoint of obtaining appropriatewater-solubility and stability of the aqueous dispersion, and M ispreferably H or NH₄ from the viewpoint of being less likely to remain asimpurities and improving the heat resistance of the resulting moldedbody.

Examples of the perfluorovinylalkyl compound represented by the formula(5b) include CH₂═CFCF₂OCF(CF₃)COOM and CH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)COOM,wherein M is as defined above.

Examples of the monomer represented by the general formula (5) furtherinclude a monomer represented by the following general formula (5c):

CF₂═CFCF₂—O—Rf—Y³  (5c)

wherein Rf and Y³ are as described above.

More specific examples thereof include:

In the general formula (6), each X is —H or —F. X may be both —F, or atleast one thereof may be —H. For example, one thereof may be —F and theother may be —H, or both may be —H.

In the general formula (6), Y is —H, —F, an alkyl group, or afluorine-containing alkyl group.

The alkyl group is an alkyl group free from fluorine atoms and may haveone or more carbon atoms. The alkyl group preferably has 6 or lesscarbon atoms, more preferably 4 or less carbon atoms, and still morepreferably 3 or less carbon atoms.

The fluorine-containing alkyl group is an alkyl group containing atleast one fluorine atom, and may have one or more carbon atoms. Thefluorine-containing alkyl group preferably has 6 or less carbon atoms,more preferably 4 or less carbon atoms, and still more preferably 3 orless carbon atoms.

Y is preferably —H, —F, or —CF₃, and more preferably —F.

In the general formula (6), at least one of X and Y preferably containsa fluorine atom. For example, X, Y, and Z may be H, F, and F,respectively.

In the general formula (6), Rf is a fluorine-containing alkylene grouphaving 1 to 40 carbon atoms or a fluorine-containing alkylene grouphaving 2 to 100 carbon atoms and having an ether bond. Thefluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond is an alkylene group which does not include astructure wherein an oxygen atom is an end and which contains an etherbond between carbon atoms.

The fluorine-containing alkylene group preferably has 2 or more carbonatoms. Further, the fluorine-containing alkylene group preferably has 30or less, more preferably 20 or less, and still more preferably 10 orless carbon atoms. Examples of the fluorine-containing alkylene groupinclude —CF₂—, —CH₂CF₂—, —CF₂CF₂—, —CF₂CH₂—, —CF₂CF₂CH₂—, —CF(CF₃)—,—CF(CF₃)CF₂—, and —CF(CF₃)CH₂—. The fluorine-containing alkylene groupis preferably a perfluoroalkylene group.

The monomer represented by the general formula (6) is preferably atleast one selected from the group consisting of monomers represented bythe following general formulas (6a), (6b), (6c), (6d), and (6e):

CF₂═CF—O—(CF₂)_(n1)—Y³  (6a)

wherein n1 represents an integer of 1 to 10, Y³ is —COOM, —SO₃M, or—OSO₃M, wherein M is H, a metal atom, NR^(7y) ₄, imidazolium optionallyhaving a substituent, pyridinium optionally having a substituent, orphosphonium optionally having a substituent, wherein R^(7y) is H or anorganic group and may be the same or different, and any two thereof maybe bonded to each other to form a ring.

CF₂═CF—O—(CF₂C(CF₃)F)_(n2)—Y³  (6b)

wherein n2 represents an integer of 1 to 5, and Y³ is as defined above;

CF₂═CF—O—(CFX¹)_(n3)—Y³  (6c)

wherein X¹ represents F or CF₃; n3 represents an integer of 1 to 10; andY³ is as defined above; and

CF₂═CF—O—(CF₂CFX¹O)_(n4)—(CF₂)_(n6)—Y³  (6d)

wherein n4 represents an integer of 1 to 10; n6 represents an integer of1 or 2; and Y³ and X¹ are as defined above.

CF₂═CF—O—(CF₂CF₂CFX¹O)_(n5)—CF₂CF₂CF₂—Y³  (6e)

wherein n5 represents an integer of 0 to 10, and Y³ and X¹ are the sameas defined above.

In the formula (6a), n1 is preferably an integer of 5 or less, and morepreferably an integer of 2 or less. Y³ is preferably —COOM from theviewpoint of obtaining appropriate water-solubility and stability of theaqueous dispersion, and M is preferably H or NH₄ from the viewpoint ofbeing less likely to remain as impurities and improving the heatresistance of the resulting molded body.

Examples of the monomer represented by the formula (6a) includeCF₂═CF—O—CF₂COOM, CF₂═CF(OCF₂CF₂COOM), and CF₂═CF(O(CF₂)₃COOM) (wherein,M is the same as defined above).

In the formula (6b), n2 is preferably an integer of 3 or less from theviewpoint of stability of the resulting aqueous dispersion, Y³ ispreferably —COOM from the viewpoint of obtaining appropriatewater-solubility and stability of the aqueous dispersion, and M ispreferably H or NH₄ from the viewpoint of being less likely to remain asimpurities and improving the heat resistance of the resulting moldedbody.

In the formula (6c), n3 is preferably an integer of 5 or less from theviewpoint of water-solubility, Y³ is preferably —COOM from the viewpointof obtaining appropriate water-solubility and stability of the aqueousdispersion, and M is preferably H or NH₄ from the viewpoint of improvingdispersion stability.

In the formula (6d), X¹ is preferably —CF₃ from the viewpoint ofstability of the aqueous dispersion, n4 is preferably an integer of 5 orless from the viewpoint of water-solubility, Y³ is preferably —COOM fromthe viewpoint of obtaining appropriate water-solubility and stability ofthe aqueous dispersion, and M is preferably H or NH₄.

Examples of the monomer represented by the formula (6d) includeCF₂═CFOCF₂CF(CF₃)OCF₂CF₂COOM and CF₂═CFOCF₂CF(CF₃)OCF₂COOM (wherein Mrepresents H, NH₄, or an alkali metal).

In the general formula (6e), n5 is preferably an integer of 5 or less interms of water solubility, Y³ is preferably —COOM in terms of obtainingmoderate water solubility and stability of the aqueous dispersion, and Mis preferably H or NH₄.

Examples of the monomer represented by the general formula (6e) includeCF₂═CFOCF₂CF₂CF₂COOM (wherein M represents H, NH₄, or an alkali metal).

In the general formula (7), Rf is preferably a fluorine-containingalkylene group having 1 to 40 carbon atoms. In the general formula (7),at least one of X and Y preferably contains a fluorine atom.

The monomer represented by the general formula (7) is preferably atleast one selected from the group consisting of:

a monomer represented by the following general formula (7a):

CF₂═CF—(CF₂)_(n)—Y³  (7a)

wherein n1 represents an integer of 1 to 10; and Y³ is as defined above;and a monomer represented by the following general formula (7b):

CF₂═CF—(CF₂C(CF₃)F)_(n2)—Y³  (7b)

wherein n2 represents an integer of 1 to 5; and Y³ is as defined above.

Y³ is preferably —SO₃M or —COOM, and M is preferably H, a metal atom,NR⁷ ₄, imidazolium optionally having a substituent, pyridiniumoptionally having a substituent, or phosphonium optionally having asubstituent. R^(7y) represents H or an organic group.

In the formula (7a), n1 is preferably an integer of 5 or less, and morepreferably an integer of 2 or less. Y³ is preferably —COOM from theviewpoint of obtaining appropriate water-solubility and stability of theaqueous dispersion, and M is preferably H or NH₄ from the viewpoint ofbeing less likely to remain as impurities and improving the heatresistance of the resulting molded body.

Examples of the perfluorovinylalkyl compound represented by the formula(7a) include CF₂═CFCF₂COOM, wherein M is as defined above.

In the formula (7b), n2 is preferably an integer of 3 or less from theviewpoint of stability of the resulting aqueous dispersion, Y³ ispreferably —COOM from the viewpoint of obtaining appropriatewater-solubility and stability of the aqueous dispersion, and M ispreferably H or NH₄ from the viewpoint of being less likely to remain asimpurities and improving the heat resistance of the resulting moldedbody.

The modifying monomer preferably contains a modifying monomer (A), andpreferably contains at least one selected from the group consisting ofcompounds represented by the general formulas (5a), (5c), (6a), (6b),(6c), and (6d), and more preferably contains a compound represented bythe general formula (5a) or (5c).

The amount of the modifying monomer (A) used is preferably an amountexceeding 0.1 mass ppm of the aqueous medium, more preferably an amountexceeding 0.5 mass ppm, still more preferably an amount exceeding 1.0mass ppm, further preferably 5 mass ppm or more, and particularlypreferably 10 mass ppm or more. When the amount of the modifying monomer(A) used is too small, the average primary particle size of the obtainedPTFE may not be reduced.

The amount of the modifying monomer (A) used may be in the above range,but the upper limit may be, for example, 5,000 mass ppm. Further, in theproduction method, the modifying monomer (A) may be added to the systemduring the reaction in order to improve the stability of the aqueousdispersion during or after the reaction.

Since the modifying monomer (A) is highly water-soluble, even if theunreacted modifying monomer (A) remains in the aqueous dispersion, itcan be easily removed in the concentration step or thecoagulation/washing step.

The modifying monomer (A) is incorporated into the resulting polymer inthe process of polymerization, but the concentration of the modifyingmonomer (A) in the polymerization system itself is low and the amountincorporated into the polymer is small, so that there is no problem thatthe heat resistance of PTFE is lowered or PTFE is colored aftersintering.

In the modified PTFE obtained by the production method of the presentdisclosure, the content of the modifying monomer (A) unit based on themodifying monomer (A) is preferably in the range of 0.00001 to 1.0% bymass based on all polymerization units of the modified PTFE. The lowerlimit thereof is more preferably 0.0001% by mass, more preferably0.0005% by mass, still more preferably 0.001% by mass, furtherpreferably 0.005% by mass, and particularly preferably 0.009% by mass.The upper limit thereof is 0.90% by mass, 0.50% by mass, 0.40% by mass,0.30% by mass, 0.20% by mass, 0.15% by mass, 0.10% by mass, 0.08% bymass, 0.05% by mass, and 0.01% by mass in the order of preference.

The average primary particle size of the modified PTFE is preferably 500nm or less, more preferably 400 nm or less, and still more preferably350 nm or less. By the production method of the present disclosure,modified PTFE having a small average primary particle size can beobtained. The lower limit of the average primary particle size may be,for example, but not limited to, 50 nm or 100 nm. From the viewpoint ofmolecular weight, it is preferably 100 nm or more, and more preferably150 nm or more.

The average primary particle size of primary particles of the modifiedPTFE obtained by the production method of the present disclosure isdetermined by diluting an aqueous dispersion of the modified PTFE withwater to a solid content of 0.15% by mass, measuring the transmittanceof projected light at 550 nm to the unit length of the obtained dilutedlatex, and measuring the number-reference length average particle sizedetermined by measuring the directional diameter by transmissionelectron microscope to prepare a calibration curve, and determining theprimary particle size from the measured transmittance of projected lightof 550 nm of each sample using the calibration curve.

Further, the average primary particle size can be determined by dynamiclight scattering. The average primary particle size may be determined bypreparing an aqueous dispersion with a solids concentration beingadjusted to 1.0% by mass and using dynamic light scattering at 25° C.with 70 measurement processes, wherein the solvent (water) has arefractive index of 1.3328 and the solvent (water) has a viscosity of0.8878 mPa·s. Dynamic light scattering may be performed by, for example,ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.).

The aspect ratio of the primary particles of the modified PTFE ispreferably less than 2.00, more preferably 1.90 or less, still morepreferably 1.80 or less, further preferably 1.70 or less, still furtherpreferably 1.60 or less, and particularly preferably 1.50 or less. Theaspect ratio is more preferably 1.45 or less, still more preferably 1.40or less, further preferably 1.35 or less, still further preferably 1.30or less, particularly preferably 1.20 or less, and most preferably 1.10or less.

When measuring in an aqueous dispersion, the aspect ratio is determinedby observing an aqueous dispersion of the modified PTFE diluted to havea solid content concentration of about 1% by mass with a scanningelectron microscope (SEM), performing image processing on 400 or moreparticles selected at random, and averaging the ratios of the major axisto the minor axis. When measuring a powder of the modified PTFE, theaspect ratio is obtained by irradiating a powder of the modified PTFEwith an electron beam, adding the powder of the modified PTFE to anaqueous solution of a fluorosurfactant, and redispersing the powder ofthe modified PTFE with ultrasonic waves to obtain an aqueous dispersionof the modified PTFE. The aspect ratio is determined from the aqueousdispersion of the modified PTFE by the same method as the method formeasuring the above aqueous dispersion.

In other words, when the aspect ratio of the modified PTFE is measuredusing an aqueous dispersion of the modified PTFE, the aspect ratio canbe determined by preparing and observing the aqueous dispersion of themodified PTFE adjusted to have a polymer solid concentration of about1.0% by mass with a scanning electron microscope (SEM), performing imageprocessing on 400 or more particles selected at random, and averagingthe ratios of the major axis to the minor axis. When the aspect ratio ofthe modified PTFE is measured by using a powder of PTFE, an aqueousdispersion of the modified PTFE is prepared by irradiating the powder ofthe modified PTFE with an electron beam, adding the modified PTFE to anaqueous solution of a fluorine-containing surfactant, and redispersingthe powder of the modified PTFE into the aqueous solution by applyingultrasonic waves. Using the aqueous dispersion prepared in this manner,the aspect ratio can be determined by the above method.

The modified PTFE preferably has a standard specific gravity (SSG) of2.280 or less, more preferably 2.250 or less, still more preferably2.210 or less, further preferably 2.200 or less, still furtherpreferably 2.190 or less, and particularly preferably 2.180 or less.Further, the standard specific gravity is preferably 2.130 or more. TheSSG is determined by the water replacement method in conformity withASTM D 792 using a sample molded in conformity with ASTM D 4895-89.

The modified PTFE preferably has an endothermic peak temperature in therange of 333 to 347° C. More preferably, the endothermic peaktemperature is 335° C. or more and 345° C. or less.

The endothermic peak temperature is a temperature corresponding to themaximum value in the heat-of-fusion curve when PTFE having no history ofbeing heated to a temperature of 300° C. or more is heated at a rate of10° C./min using a differential scanning calorimeter (DSC).

The extrusion pressure of the modified PTFE is preferably 50.0 MPa orlower, more preferably 40.0 MPa or lower, and preferably 5.0 MPa orhigher, more preferably 10.0 MPa or higher, and still more preferably15.0 MPa or higher.

The extrusion pressure is a value determined by the following method. To100 g of a powder of the modified PTFE, 21.7 g of a lubricant (tradename: Isopar H®, manufactured by Exxon) is added and mixed for 3 minutesin a glass bottle at room temperature. Then, the glass bottle is left tostand at room temperature (25° C.) for at least 1 hour before extrusionto obtain a lubricated resin. The lubricated resin is paste extruded ata reduction ratio of 100:1 at room temperature through an orifice(diameter 2.5 mm, land length 11 nm, entrance angle 30°) into a uniformbeading. The extrusion speed, i.e. ram speed, is 20 inch/min (51cm/min). The extrusion pressure is a value obtained by measuring theload when the extrusion load becomes balanced in the paste extrusion anddividing the measured load by the cross-sectional area of the cylinderused in the paste extrusion.

The modified PTFE is usually stretchable, fibrillatable and non-moltensecondary processible. The non-molten secondary processible means aproperty that the melt flow rate cannot be measured at a temperaturehigher than the crystal melting point, that is, a property that does noteasily flow even in the melting temperature region, in conformity withASTM D 1238 and D 2116.

The modified PTFE may have a core-shell structure. The core-shellstructure is a conventionally known structure, and is a structure ofprimary particles in an aqueous dispersion that can be produced by themethod or the like described in U.S. Pat. No. 6,841,594.

Examples of PTFE having a core-shell structure include a core-shellstructure including a core portion of a TFE homopolymer and a shellportion of modified PTFE, a core-shell structure including a coreportion of modified PTFE and a shell portion of a TFE homopolymer, and acore-shell structure including a core portion of modified PTFE and ashell portion of modified PTFE having a monomer composition differentfrom that of modified PTFE constituting the core portion.

PTFE having a core-shell structure can be obtained, for example, byfirst polymerizing TFE and optionally a modifying monomer to produce acore portion (TFE homopolymer or modified PTFE), and then polymerizingTFE and optionally a modifying monomer to produce a shell portion (TFEhomopolymer or modified PTFE).

The shell portion means a portion constituting a predetermined thicknessfrom the surface of a PTFE primary particle to the inside of theparticle, and the core portion means a portion constituting the insideof the shell portion.

In the present disclosure, the core-shell structure includes all of (1)a core-shell structure including a core portion and a shell portionhaving different monomer compositions, (2) a core-shell structureincluding a core portion and a shell portion having the same monomercomposition with different number average molecular weights in bothportions, and (3) a core-shell structure including a core portion and ashell portion having different monomer compositions with differentnumber average molecular weights in both portions.

When the shell portion is modified PTFE, the content of the modifyingmonomer in the shell portion is preferably 0.0001 to 1% by mass. Thecontent thereof is more preferably 0.001% by mass or more, and stillmore preferably 0.01% by mass or more. Further, the content thereof ismore preferably 0.50% by mass or less, and still more preferably 0.30%by mass or less.

When the core portion is modified PTFE, the content of the modifyingmonomer in the core portion is preferably 0.00001 to 1.0% by mass. Thecontent thereof is more preferably 0.0001% by mass or more, and stillmore preferably 0.001% by mass or less. Further, the content thereof ismore preferably 0.50% by mass or less, and still more preferably 0.30%by mass or less.

The PTFE may have a thermal instability index (TII) of 20 or more. Thethermal instability index (TII) of PTFE can be adjusted within the aboverange, for example, by producing PTFE using the polymer (I). The TII ispreferably 25 or more, more preferably 30 or more, and still morepreferably 35 or more. The TII is particularly preferably 40 or more.The TII is measured in conformity with ASTM D 4895-89.

PTFE may have a 0.1% mass loss temperature of 400° C. or lower. The 0.1%mass loss temperature of PTFE can be adjusted within the above range,for example, by producing PTFE using the polymer (I).

The 0.1% mass loss temperature can be measured using TG/DTA(thermogravimetric-differential thermal analyzer) by precisely weighingabout 10 mg of PTFE powder, which has no history of being heated to atemperature of 300° C. or higher, and storing it in a dedicated aluminumpan. The 0.1% mass loss temperature can be specified as a temperaturecorresponding to the point at which the mass of the aluminum pan isreduced by 0.1% by mass by heating the aluminum pan under the conditionof 10° C./min in the temperature range from 25° C. to 600° C. in the airatmosphere.

PTFE may have a 1.0% mass loss temperature of 492° C. or lower. The 0.1%mass loss temperature of PTFE can be adjusted within the above range,for example, by producing PTFE using the polymer (I).

The 1.0% mass loss temperature can be measured using TG/DTA(thermogravimetric-differential thermal analyzer) by precisely weighingabout 10 mg of PTFE powder, which has no history of being heated to atemperature of 300° C. or higher, and storing it in a dedicated aluminumpan. The 1.0% mass loss temperature can be specified as a temperaturecorresponding to the point at which the mass of the aluminum pan isreduced by 1.0% by mass by heating the aluminum pan under the conditionof 10° C./min in the temperature range from 25° C. to 600° C. in the airatmosphere.

The polymer (I) used in the production method of the present disclosurecontains a polymerization unit (I) based on a monomer represented by thefollowing general formula (I). The polymer (I) preferably contains twoor more polymerization units (I):

CX¹X³═CX²R(—CZ¹Z²-A⁰)_(m)  (I)

wherein X¹ and X³ are each independently F, Cl, H, or CF₃; X² is H, F,an alkyl group, or a fluorine-containing alkyl group; A⁰ is an anionicgroup; R is a linking group; Z¹ and Z² are each independently H, F, analkyl group, or a fluorine-containing alkyl group; and m is an integerof 1 or more.

X² is preferably F, Cl, H, or CF₃. Further, Z¹ and Z² are preferably For CF₃.

In the present disclosure, the anionic group includes a functional groupthat imparts an anionic group, e.g., an acid group such as —COOH and anacid base such as —COONH₄, in addition to anionic groups such as asulfate group and a carboxylate group. The anionic group is preferably asulfate group, a carboxylate group, a phosphate group, a phosphonategroup, a sulfonate group, or —C(CF₃)₂OM (wherein M is —H, a metal atom,—NR⁷ ₄, imidazolium optionally having a substituent, pyridiniumoptionally having a substituent, or phosphonium optionally having asubstituent, and R⁷ is H or an organic group), and more preferably asulfate group, a carboxylate group, a phosphate group, a phosphonategroup, or a sulfonate group.

The polymer (I) may contain the polymerization unit (I) that is basedsolely on one monomer represented by the general formula (I), or maycontain the polymerization unit (I) based on two or more monomersrepresented by the general formula (I).

R is a linking group. The “linking group” as used herein is a(m+1)-valent linking group, and refers to a divalent group when m is 1.The linking group may be a single bond and preferably contains at leastone carbon atom, and the number of carbon atoms may be 2 or more, 4 ormore, 8 or more, 10 or more, or 20 or more. The upper limit thereof isnot limited, but may be 100 or less, and may be 50 or less, for example.

The linking group may be linear or branched, cyclic or acyclic,saturated or unsaturated, substituted or unsubstituted, and optionallycontains one or more heteroatoms selected from the group consisting ofsulfur, oxygen, and nitrogen, and optionally contains one or morefunctional groups selected from the group consisting of esters, amides,sulfonamides, carbonyls, carbonates, urethanes, ureas and carbamates.The linking group may be free from carbon atoms and may be a catenaryheteroatom such as oxygen, sulfur, or nitrogen.

m is an integer of 1 or more and is preferably 1 or 2 and morepreferably 1. When m is an integer of 2 or more, Z¹, Z², and A⁰ may bethe same or different. Next, a suitable configuration wherein m is 1 inthe general formula (I) will now be described.

R is preferably a catenary heteroatom such as oxygen, sulfur, ornitrogen, or a divalent organic group.

When R is a divalent organic group, the hydrogen atom bonded to thecarbon atom may be replaced by a halogen other than fluorine, such aschlorine, and may or may not contain a double bond. Further, R may belinear or branched, and may be cyclic or acyclic. R may also contain afunctional group (e.g., ester, ether, ketone, amine, halide, etc.).

R may also be a fluorine-free divalent organic group or a partiallyfluorinated or perfluorinated divalent organic group.

R may be, for example, a hydrocarbon group in which a fluorine atom isnot bonded to a carbon atom, a hydrocarbon group in which some of thehydrogen atoms bonded to a carbon atom are replaced by fluorine atoms,or a hydrocarbon group in which all of the hydrogen atoms bonded to thecarbon atoms are replaced by fluorine atoms, and these groups optionallycontain an oxygen atom, optionally contain a double bond, and optionallycontain a functional group.

R is preferably a hydrocarbon group having 1 to 100 carbon atoms thatoptionally contains an ether bond, wherein some or all of the hydrogenatoms bonded to the carbon atoms in the hydrocarbon group may bereplaced by fluorine.

R is preferably at least one selected from —(CH₂)_(a)—, —(CF₂)_(a)—,—O—(CF₂)_(a)—, —(CF₂)_(a)—O—(CF₂)_(b)—, —O(CF₂)_(a)—O—(CF₂)_(b)—,—(CF₂)_(a)—[O—(CF₂)_(b)]_(c)—, —O(CF₂)_(a)—[O—(CF₂)_(b)]_(c)—,—[(CF₂)_(a)—O]_(b)—[(CF₂)_(c)—O]_(d)—,—O[(CF₂)_(a)—O]_(b)—[(CF₂)_(c)—O]_(d)—, —O—[CF₂CF(CF₃)O]_(a)—(CF₂)_(b)—,—[CF₂CF(CF₃)O]_(a)—, —[CF(CF₃)CF₂O]_(a)—,—(CF₂)_(a)—O—[CF(CF₃)CF₂O]_(a)—,—(CF₂)_(a)—O—[CF(CF₃)CF₂O]_(a)—(CF₂)_(b)—, and combinations thereof.

In the formula, a, b, c, and d are independently at least 1 or more. a,b, c and d may independently be 2 or more, 3 or more, 4 or more, 10 ormore, or 20 or more. The upper limits of a, b, c, and d are 100, forexample.

R is preferably a divalent group represented by the following generalformula (r1):

(C═O)_(h)—(O)_(i)—CF₂—O—(CX⁶ ₂)_(e)—{O—CF(CF₃)}_(f)—(O)_(g)—  (r1)

wherein X⁶ is each independently H, F, or CF₃; e is an integer of 0 to3; f is an integer of 0 to 3; and g is 0 or 1, and is also preferably adivalent group represented by the following general formula (r2):

(C═O)_(h)—(O)_(i)—CF₂—O—(CX⁷ ₂)_(e)—(O)_(g)—  (r2)

wherein X⁷ is each independently H, F, or CF₃; e is an integer of 0 to3; and g is 0 or 1.

Specific examples suitable for R include —CF₂—O—, —CF₂—O—CF₂—,—CF₂—O—CH₂—, —CF₂—O—CH₂CF₂—, —CF₂—O—CF₂CF₂—, —CF₂—O—CF₂CH₂—,—CF₂—O—CF₂CF₂CH₂—, —CF₂—O—CF(CF₃)—, —CF₂—O—CF(CF₃)CF₂—,—CF₂—O—CF(CF₃)CF₂—O—, —CF₂—O—CF(CF₃)CF₂—O—CF₂—, and —CF₂—O—CF(CF₃)CH₂—.In particular, R is preferably a perfluoroalkylene group optionallycontaining an oxygen atom, and, specifically, —CF₂—O—, —CF₂—O—CF₂—,—CF₂—O—CF₂CF₂—, —CF₂—O—CF(CF₃)—, —CF₂—O—CF(CF₃)CF₂—, or—CF₂—O—CF(CF₃)CF₂—O— is preferable.

—R—CZ¹Z²— in the general formula (I) is preferably represented by thefollowing formula (s1):

—CF₂—O—(CX⁶ ₂)_(e)—{O—CF(CF₃)}—(O)_(g)—CZ¹Z²—  (s1)

(wherein X⁶ is each independently H, F, or CF₃; e is an integer of 0 to3; f is an integer of 0 to 3; g is 0 or 1; and Z¹ and Z² are eachindependently H, F, an alkyl group, or a fluorine-containing alkylgroup), and more preferably, in the formula (s1), Z¹ and Z² are F orCF₃, and further preferably one is F and the other is CF₃.

Further, —R—CZ¹Z²— in the general formula (I) is preferably representedby the following formula (s2):

—CF₂—O—(CX⁷ ₂)_(e)—(O)_(g)—CZ¹Z²—  (s2)

(wherein X⁷ is each independently H, F, or CF₃; e is an integer of 0 to3; g is 0 or 1; and Z¹ and Z² are each independently F or CF₃), and ismore preferably a group in which one of Z¹ and Z² is F and the other isCF₃ in the formula (s2).

—R—CZ¹Z²— in the above general formula (I) is preferably —CF₂—O—CF₂—,—CF₂—O—CF(CF₃)—, —CF₂—O—C(CF₃)₂—, —CF₂—O—CF₂—CF₂—, —CF₂—O—CF₂—CF(CF₃)—,—CF₂—O—CF₂—C(CF₃)₂—, —CF₂—O—CF₂CF₂—CF₂—, —CF₂—O—CF₂CF₂—CF(CF₃)—,—CF₂—O—CF₂CF₂—C(CF₃)₂—, —CF₂—O—CF(CF₃)—CF₂—, —CF₂—O—CF(CF₃)—CF(CF₃)—,—CF₂—O—CF(CF₃)—C(CF₃)₂—, —CF₂—O—CF(CF₃)—CF₂—, —CF₂—O—CF(CF₃)—CF(CF₃)—,—CF₂—O—CF(CF₃)—C(CF₃)₂—, —CF₂—O—CF(CF₃)CF₂—CF₂—,—CF₂—O—CF(CF₃)CF₂—CF(CF₃)—, —CF₂—O—CF(CF₃)CF₂—C(CF₃)₂—,—CF₂—O—CF(CF₃)CF₂—O—CF₂—, —CF₂—O—CF(CF₃)CF₂—O—CF(CF₃)—, or—CF₂—O—CF(CF₃)CF₂—O—C(CF₃)₂—, and more preferably —CF₂—O—CF(CF₃)—,—CF₂—O—CF₂—CF(CF₃)—, —CF₂—O—CF₂CF₂—CF(CF₃)—, —CF₂—O—CF(CF₃)—CF(CF₃)—,—CF₂—O—CF(CF₃)CF₂—CF(CF₃)—, or —CF₂—O—CF(CF₃)CF₂—O—CF(CF₃)—.

It is also preferable that the polymer (I) is highly fluorinated. Exceptfor the anionic group (A⁰) such as a phosphate group moiety (such asCH₂OP(O)(CM)₂) and a sulfate group moiety (such as CH₂OS(O)₂OM), 80% ormore, 90% or more, 95% or more, or 100% of C—H bonds in the polymer (I)are replaced with C—F bonds.

The polymer (I) also preferably has a C—F bond and does not have a C—Hbond, in the portion excluding the anionic group (A⁰). In other words,in the general formula (I), X¹, X², and X³ are all F, and R ispreferably a perfluoroalkylene group having one or more carbon atoms;the perfluoroalkylene group may be either linear or branched, may beeither cyclic or acyclic, and may contain at least one catenaryheteroatom. The perfluoroalkylene group may have 2 to 20 carbon atoms or4 to 18 carbon atoms.

The polymer (I) may be partially fluorinated. In other words, thepolymer (I) also preferably has at least one hydrogen atom bonded to acarbon atom and at least one fluorine atom bonded to a carbon atom, inthe portion excluding the anionic group (A⁰).

The anionic group (A⁰) may be —SO₃M, —OSO₃M, —COOM, —SO₂NR′CH₂COOM,—CH₂OP(O)(OM)₂, [—CH₂O]₂P(O)(OM), —CH₂CH₂OP(O)(CM)₂,[—CH₂CH₂O]₂P(O)(OM), —CH₂CH₂OSO₃M, —P(O)(CM)₂, —SO₂NR′CH₂CH₂OP(O)(OM)₂,[—SO₂NR′CH₂CH₂O]₂P(O)(CM), —CH₂OSO₃M, —SO₂NR′CH₂CH₂OSO₃M, or —C(CF₃)₂OM.Among these, —SO₃M, —COOM, or —P(O)(CM)₂ is preferable, —SO₃M or —COOMis more preferable, and —COOM is still more preferable.

M is —H, a metal atom, —NR⁷ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent, and R⁷ is H or an organic group.

Examples of the metal atom include alkali metals (Group 1) and alkalineearth metals (Group 2), and preferred is Na, K, or Li.

M is preferably —H, a metal atom, or —NR⁷ ₄, more preferably —H, analkali metal (Group 1), an alkaline earth metal (Group 2), or —NR⁷ ₄,still more preferably —H, —Na, —K, —Li, or —NH₄, further preferably —Na,—K, or —NH₄, particularly preferably —Na or —NH₄, and most preferably—NH₄.

In the polymer (I), each polymerization unit (I) may have a differentanionic group or may have the same anionic group.

The polymer (I) is also preferably a polymer containing a polymerizationunit (Ia) based on a monomer represented by the following formula (Ia):

CF₂═CF—O—Rf⁰-A⁰  (Ia)

wherein A⁰ is an anionic group; and Rf⁰ is a perfluorinated divalentlinking group which is perfluorinated and may be a linear or branched,cyclic or acyclic, saturated or unsaturated, substituted orunsubstituted, and optionally contains one or more heteroatoms selectedfrom the group consisting of sulfur, oxygen, and nitrogen.

The polymer (I) is also preferably a polymer containing a polymerizationunit (Ib) based on a monomer represented by the following formula (Ib):

CH₂═CH—O—Rf⁰-A⁰  (Ib)

wherein A⁰ is an anionic group, and Rf⁰ is a perfluorinated divalentlinking group as defined by formula (Ia).

In a preferred embodiment, in the general formula (I), A⁰ is a sulfategroup. A⁰ is, for example, —CH₂OSO₃M, —CH₂CH₂OSO₃M, or—SO₂NR′CH₂CH₂OSO₃M, wherein R′ is H or an alkyl group having 1 to 4carbon atoms, and M is the same as above.

When A⁰ is a sulfate group, examples of the monomer represented by thegeneral formula (I) include CF₂═CF(OCF₂CF₂CH₂OSO₃M),CH₂═CH((CF₂)₄CH₂OSO₃M), CF₂═CF(O(CF₂)₄CH₂OSO₃M),CF₂═CF(OCF₂CF(CF₃)CH₂OSO₃M), CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂CH₂OSO₃M),CH₂═CH((CF₂)₄CH₂OSO₃M), CF₂═CF(OCF₂CF₂SO₂N(CH₃)CH₂CH₂OSO₃M),CH₂═CH(CF₂CF₂CH₂OSO₃M), CF₂═CF(OCF₂CF₂CF₂CF₂SO₂N(CH₃)CH₂CH₂OSO₃M), andCH₂═CH(CF₂CF₂CF₂CH₂OSO₃M). In the formula, M is the same as above.

In a preferred embodiment, in the general formula (I), A⁰ is a sulfonategroup. A⁰ is, for example, —SO₃M, wherein M is the same as above.

When A⁰ is a sulfonate group, examples of the monomer represented by thegeneral formula (I) include CF₂═CF(OCF₂CF₂SO₃M), CF₂═CF(O(CF₂)₃SO₃M),CF₂═CF(O(CF₂)₄SO₃M), CF₂═CF(OCF₂CF(CF₃) SO₃M),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂SO₃M), CH₂═CH(CF₂CF₂SO₃M),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂CF₂CF₂SO₃M), CH₂═CH((CF₂)₄SO₃M),CH₂═CH(CF₂CF₂SO₃M), and CH₂═CH((CF₂)₃SO₃M). In the formula, M is thesame as above.

In a preferred embodiment, in the general formula (I), A⁰ is acarboxylate group. A⁰ is, for example, —COOM or —SO₂NR′CH₂COOM, whereinR′ is H or an alkyl group having 1 to 4 carbon atoms, and M is the sameas above. When A⁰ is a carboxylate group, examples of the polymerizationunit (I) include CF₂═CF(OCF₂CF₂COOM), CF₂═CF(O(CF₂)₃COOM),CF₂═CF(O(CF₂)₄COOM), CF₂═CF(O(CF₂)₅COOM), CF₂═CF(OCF₂CF(CF₃)COOM),CF₂═CF(OCF₂CF(CF₃)O(CF₂)_(n)COOM) (wherein n is greater than 1),CH₂═CH(CF₂CF₂COOM), CH₂═CH((CF₂)₄COOM), CH₂═CH(CF₂CF₂COOM),CH₂═CH((CF₂)₃COOM), CF₂═CF(OCF₂CF₂SO₂NR′CH₂COOM),CF₂═CF(O(CF₂)₄SO₂NR′CH₂COOM), CF₂═CF(OCF₂CF(CF₃) SO₂NR′CH₂COOM),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂SO₂NR′CH₂COOM), CH₂═CH(CF₂CF₂SO₂NR′CH₂COOM),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂CF₂CF₂SO₂NR′CH₂COOM),CH₂═CH((CF₂)₄SO₂NR′CH₂COOM), CH₂═CH(CF₂CF₂SO₂NR′CH₂COOM), andCH₂═CH((CF₂)₃SO₂NR′CH₂COOM). In the formula, R′ is an H or C₁₋₄ alkylgroup, and M is the same as above.

In a preferred embodiment, in the general formula (I), A⁰ is a phosphategroup. A⁰ is, for example, —CH₂OP(O)(OM)₂, [—CH₂O]₂P(O)(OM),—CH₂CH₂OP(O)(OM)₂, [—CH₂CH₂O]₂P(O)(OM), [—SO₂NR′CH₂CH₂O]₂P(O)(OM), or—SO₂NR′CH₂CH₂OP(O)(OM)₂, wherein R′ is a C₁₋₄ alkyl group, and M is thesame as above. When A⁰ is a phosphate group, examples of the monomerrepresented by the general formula (I) includeCF₂═CF(OCF₂CF₂CH₂OP(O)(OM)₂), CF₂═CF(O(CF₂)₄CH₂OP(O)(OM)₂),CF₂═CF(OCF₂CF(CF₃)CH₂OP(O)(CM)₂),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂CH₂OP(O)(CM)₂),CF₂═CF(OCF₂CF₂SO₂N(CH₃)CH₂CH₂OP(O)(OM)₂),CF₂═CF(OCF₂CF₂CF₂CF₂SO₂N(CH₃)CH₂CH₂OP(O)(OM)₂),CH₂═CH(CF₂CF₂CH₂OP(O)(CM)₂), CH₂═CH((CF₂)₄CH₂OP(O)(OM)₂),CH₂═CH(CF₂CF₂CH₂OP(O)(CM)₂), and CH₂═CH((CF₂)₃CH₂OP(O)(OM)₂). In theformula, M is the same as above.

In the general formula (I), A⁰ is preferably a phosphonate group. WhenA⁰ is a phosphonate group, examples of the monomer represented by thegeneral formula (I) include CF₂═CF(OCF₂CF₂P(O)(OM)₂),CF₂═CF(O(CF₂)₄P(O)(OM)₂), CF₂═CF(OCF₂CF(CF₃) P(O)(OM)₂),CF₂═CF(OCF₂CF(CF₃)OCF₂CF₂P(O)(OM)₂), CH₂═CH(CF₂CF₂P(O)(OM)₂),CH₂═CH((CF₂)₄P(O)(CM)₂), CH₂═CH(CF₂CF₂P(O)(CM)₂), andCH₂═CH((CF₂)₃P(O)(OM)₂), wherein M is the same as above.

The polymer (I) is preferably a polymer (1) containing a polymerizationunit (1) based on a monomer represented by the following formula (1):

CX²═CY(—CZ₂—O—Rf-A)  (1)

wherein X is the same or different and is —H or —F; Y is —H, —F, analkyl group, or a fluorine-containing alkyl group; Z is the same ordifferent and is —H, —F, an alkyl group, or a fluoroalkyl group; Rf is afluorine-containing alkylene group having 1 to 40 carbon atoms or afluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond; A is —COOM, —SO₃M, —OSO₃M, or C(CF₃)₂OM, wherein Mis —H, a metal atom, —NR⁷ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent, and R⁷ is H or an organic group;provided that at least one of X, Y, and Z contains a fluorine atom.

By containing the polymer (1), the composition of the present disclosurecontaining modified polytetrafluoroethylene can be produced more stablyand efficiently. Further, a composition containing modifiedpolytetrafluoroethylene having a high molecular weight can be obtainedin a high yield.

The fluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond is an alkylene group which does not include astructure wherein an oxygen atom is an end and which contains an etherbond between carbon atoms.

In the general formula (1), each X is —H or —F. X may be both —F, or atleast one thereof may be —H. For example, one thereof may be —F and theother may be —H, or both may be —H.

In the general formula (1), Y is —H, —F, an alkyl group, or afluorine-containing alkyl group. The alkyl group is an alkyl group freefrom fluorine atoms and may have one or more carbon atoms. The alkylgroup preferably has 6 or less carbon atoms, more preferably 4 or lesscarbon atoms, and still more preferably 3 or less carbon atoms. Thefluorine-containing alkyl group is an alkyl group containing at leastone fluorine atom, and may have one or more carbon atoms. Thefluorine-containing alkyl group preferably has 6 or less carbon atoms,more preferably 4 or less carbon atoms, and still more preferably 3 orless carbon atoms. Y is preferably —H, —F, or —CF₃, and more preferably—F.

In the general formula (1), Z is the same or different and is —H, —F, analkyl group, or a fluoroalkyl group.

The alkyl group is an alkyl group free from fluorine atoms and may haveone or more carbon atoms. The alkyl group preferably has 6 or lesscarbon atoms, more preferably 4 or less carbon atoms, and still morepreferably 3 or less carbon atoms.

The fluorine-containing alkyl group is an alkyl group containing atleast one fluorine atom, and may have one or more carbon atoms. Thefluorine-containing alkyl group preferably has 6 or less carbon atoms,more preferably 4 or less carbon atoms, and still more preferably 3 orless carbon atoms.

Z is preferably —H, —F, or —CF₃, and more preferably —F.

In the general formula (1), at least one of X, Y, and Z contains afluorine atom. For example, X may be —H, and Y and Z may be —F.

In the general formula (1), Rf is a fluorine-containing alkylene grouphaving 1 to 40 carbon atoms or a fluorine-containing alkylene grouphaving 2 to 100 carbon atoms and having an ether bond. Thefluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond is an alkylene group which does not include astructure wherein an oxygen atom is an end and which contains an etherbond between carbon atoms.

The fluorine-containing alkylene group preferably has 2 or more carbonatoms. Further, the fluorine-containing alkylene group preferably has 30or less carbon atoms, more preferably 20 or less carbon atoms, and stillmore preferably 10 or less carbon atoms. Examples of thefluorine-containing alkylene group include —CF₂—, —CH₂CF₂—, —CF₂CF₂—,—CF₂CH₂—, —CF₂CF₂CH₂—, —CF(CF₃)—, —CF(CF₃)CF₂—, and —CF(CF₃)CH₂—. Thefluorine-containing alkylene group is preferably a perfluoroalkylenegroup.

The fluorine-containing alkylene group having an ether bond preferablyhas 3 or more carbon atoms. Further, the fluorine-containing alkylenegroup having an ether bond preferably has 60 or less, more preferably 30or less, and still more preferably 12 or less carbon atoms.

The fluorine-containing alkylene group having an ether bond is alsopreferably a divalent group represented by the following formula:

wherein Z¹ is F or CF₃; Z² and Z³ are each H or F; Z⁴ is H, F, or CF₃;p1+q1+r1 is an integer of 1 to 10; s1 is 0 or 1; and t1 is an integer of0 to 5.

Specific examples of the fluorine-containing alkylene group having anether bond include —CF(CF₃)CF₂—O—CF(CF₃)—, —(CF(CF₃)CF₂—O)_(n)—CF(CF₃)—(wherein n is an integer of 1 to 10), —CF(CF₃)CF₂—O—CF(CF₃)CH₂—,—(CF(CF₃)CF₂—O)_(n)—CF(CF₃)CH₂— (wherein n is an integer of 1 to 10),—CH₂CF₂CF₂O—CH₂CF₂CH₂—, —CF₂CF₂CF₂O—CF₂CF₂—, —CF₂CF₂CF₂O—CF₂CF₂CH₂—,—CF₂CF₂O—CF₂—, and —CF₂CF₂O—CF₂CH₂—. The fluorine-containing alkylenegroup having an ether bond is preferably a perfluoroalkylene group.

In the general formula (1), A is —COOM, —SO₃, —OSO₃M, or —C(CF₃)₂OM,wherein M is —H, a metal atom, —NR⁷ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent, and R⁷ is H or an organic group.

R⁷ is preferably H or a C₁₋₁₀ organic group, more preferably H or a C₁₋₄organic group, and still more preferably H or a C₁₋₄ alkyl group.

Examples of the metal atom include alkali metals (Group 1) and alkalineearth metals (Group 2), and preferred is Na, K, or Li.

M is preferably —H, a metal atom, or —NR⁷ ₄, more preferably —H, analkali metal (Group 1), an alkaline earth metal (Group 2), or —NR⁷ ₄,still more preferably —H, —Na, —K, —Li, or —NH₄, further preferably —Na,—K, or —NH₄, particularly preferably —Na or —NH₄, and most preferably—NH₄.

A is preferably —COOM or —SO₃M, and more preferably —COOM.

The monomer represented by the general formula (1) is preferably afluoroallyl ether compound represented by the following formula (Ia):

CX²═CFCF₂—O—(CF(CF₃)CF₂O)_(n5)—CF(CF₃)-A  (1a)

wherein each X is the same, and each represent F or H; n5 represents 0or an integer of 1 to 10; and A is as defined above.

In the general formula (1a), n5 is preferably 0 or an integer of 1 to 5,more preferably 0, 1, or 2, and still more preferably 0 or 1 from theviewpoint of obtaining PTFE particles having a small primary particlesize. A is preferably —COOM from the viewpoint of obtaining appropriatewater-solubility and surface activity, and M is preferably H or NH₄ fromthe viewpoint of being less likely to remain as impurities and improvingthe heat resistance of the resulting molded body.

The polymer (1) may be a homopolymer of the fluoroallyl ether compoundrepresented by the general formula (1a), or may be a copolymer withfurther monomer.

The monomer unit (1) is preferably a monomer unit (1A) based on amonomer represented by the following general formula (1A):

CH₂═CF(—CF₂—O—Rf-A)  (1A)

wherein Rf and A are as described above.

The polymer (1) may be a homopolymer of the monomer represented by thegeneral formula (1A), or may be a copolymer with a further monomer.

Specific examples of the monomer represented by the general formula (1A)include a monomer represented by the following formula:

wherein Z¹ is F or CF₃; Z² and Z³ are each H or F; Z⁴ is H, F, or CF₃;p1+q1+r1 is an integer of 0 to 10; s1 is 0 or 1; and t1 is an integer of0 to 5, with the proviso that when Z³ and Z⁴ are both H, p1+q1+r1+s1 isnot 0. More specifically, preferred examples thereof include:

Of these,

are preferable.

In the monomer represented by the general formula (1A), A in the formula(1A) is preferably —COOM. Specifically, the monomer represented by thegeneral formula (1A) is preferably at least one selected from the groupconsisting of CH₂═CFCF₂OCF(CF₃)COOM and CH₂═CFCF₂OCF(CF₃)CF₂OCF(CF₃)COOM(wherein M is as defined above), and more preferablyCH₂═CFCF₂OCF(CF₃)COOM.

Examples of the monomer represented by the general formula (1) furtherinclude a monomer represented by the following general formula:

CF₂═CFCF₂—O—Rf-A

wherein Rf and A are as described above.

More specific examples thereof include:

The polymer (I) is also preferably a polymer (2) containing apolymerization unit (2) based on a monomer represented by generalformula (2)

CX₂═CY(—O—Rf-A)  (2)

wherein X is the same or different and is —H or —F; Y is —H, —F, analkyl group, or a fluorine-containing alkyl group; Rf is afluorine-containing alkylene group having 1 to 40 carbon atoms or afluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond; and A is as described above.

In the general formula (2), each X is —H or —F. X may be both —F, or atleast one thereof may be —H. For example, one thereof may be —F and theother may be —H, or both may be —H.

In the general formula (2), Y is —H, —F, an alkyl group, or afluorine-containing alkyl group. The alkyl group is an alkyl group freefrom fluorine atoms and may have one or more carbon atoms. The alkylgroup preferably has 6 or less carbon atoms, more preferably 4 or lesscarbon atoms, and still more preferably 3 or less carbon atoms. Thefluorine-containing alkyl group is an alkyl group containing at leastone fluorine atom, and may have one or more carbon atoms. Thefluorine-containing alkyl group preferably has 6 or less carbon atoms,more preferably 4 or less carbon atoms, and still more preferably 3 orless carbon atoms. Y is preferably —H, —F, or —CF₃, and more preferably—F.

In the general formula (2), at least one of X and Y preferably containsa fluorine atom. For example, X may be —H, and Y and Z may be —F.

In the general formula (2), Rf is a fluorine-containing alkylene grouphaving 1 to 40 carbon atoms or a fluorine-containing alkylene grouphaving 2 to 100 carbon atoms and having an ether bond. Thefluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond is an alkylene group which does not include astructure wherein an oxygen atom is an end and which contains an etherbond between carbon atoms.

The fluorine-containing alkylene group of Rf preferably has 2 or morecarbon atoms. The fluorine-containing alkylene group also preferably has30 or less carbon atoms, more preferably 20 or less carbon atoms, andstill more preferably 10 or less carbon atoms. Examples of thefluorine-containing alkylene group include —CF₂—, —CH₂CF₂—, —CF₂CF₂—,—CF₂CH₂—, —CF₂CF₂CH₂—, —CF(CF₃)—, —CF(CF₃)CF₂—, and —CF(CF₃)CH₂—. Thefluorine-containing alkylene group is preferably a perfluoroalkylenegroup.

The monomer represented by the general formula (2) is preferably atleast one selected from the group consisting of monomers represented bythe following general formulas (2a), (2b), (2c), (2d), and (2e):

CF₂═CF—O—(CF₂)_(n1)-A  (2a)

wherein n1 represents an integer of 1 to 10, and A is as defined above;

CF₂═CF—O—(CF₂C(CF₃)F)_(n2)-A  (2b)

wherein n2 represents an integer of 1 to 5, and A is as defined above;

CF₂═CF—O—(CFX¹)_(n3)-A  (2c)

wherein X¹ represents F or CF₃; n3 represents an integer of 1 to 10; andA is as defined above;

CF₂═CF—O—(CF₂CFX¹O)_(n4)—(CF₂)_(n6)-A  (2d)

wherein n4 represents an integer of 1 to 10; n6 represents an integer of1 to 3; and A and X1 are as defined above; and

CF₂═CF—O—(CF₂CF₂CFX¹O)_(n5)—CF₂CF₂CF₂-A  (2e)

wherein n5 represents an integer of 0 to 10, and A and X¹ are as definedabove.

In the general formula (2a), n1 is preferably an integer of 5 or less,and more preferably an integer of 2 or less.

Examples of the monomer represented by the general formula (2a) includeCF₂═CF—O—CF₂COOM, CF₂═CF(OCF₂CF₂COOM), and CF₂═CF(O(CF₂)₃COOM), whereinM is as defined above.

In the general formula (2b), n2 is preferably an integer of 3 or lessfrom the viewpoint of dispersion stability of the resulting composition.

In the general formula (2c), n3 is preferably an integer of 5 or lessfrom the viewpoint of water solubility, A is preferably —COOM, and M ispreferably H or NH₄.

In the general formula (2d), X¹ is preferably —CF₃ from the viewpoint ofdispersion stability of the composition, n4 is preferably an integer of5 or less from the viewpoint of water solubility, A is preferably —COOM,and M is preferably H or NH₄.

Examples of the monomer represented by the general formula (2d) includeCF₂═CFOCF₂CF(CF₃)OCF₂CF₂COOM, CF₂═CFOCF₂CF(CF₃)OCF₂COOM, andCF₂═CFOCF₂CF(CF₃)OCF₂CF₂CF₂COOM (wherein M represents H, NH₄, or analkali metal).

In the general formula (2e), n5 is preferably an integer of 5 or lessfrom the viewpoint of water solubility, A is preferably —COOM, and M ispreferably H or NH₄.

Examples of the monomer represented by the general formula (2e) includeCF₂═CFOCF₂CF₂CF₂COOM (wherein M represents H, NH₄, or an alkali metal).

The polymer (I) is also preferably a polymer (3) containing apolymerization unit (3) based on a monomer represented by generalformula (3):

CX²═CY(—Rf-A)  (3)

wherein X is the same or different and is —H or —F; Y is —H, —F, analkyl group, or a fluorine-containing alkyl group; Rf is afluorine-containing alkylene group having 1 to 40 carbon atoms or afluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond; and A is as described above.

The fluorine-containing alkylene group having 2 to 100 carbon atoms andhaving an ether bond is an alkylene group which does not include astructure wherein an oxygen atom is an end and which contains an etherbond between carbon atoms.

In the general formula (3), Rf is preferably a fluorine-containingalkylene group having 1 to 40 carbon atoms. In the general formula (3),at least one of X and Y preferably contains a fluorine atom.

The monomer represented by the general formula (3) is preferably atleast one selected from the group consisting of a monomer represented bygeneral formula (3a):

CF₂═CF—(CF₂)_(n1)-A  (3a)

wherein n1 represents an integer of 1 to 10, and A is as defined above;and a monomer represented by general formula (3b):

CF₂═CF—(CF₂C(CF₃)F)_(n2)-A  (3b)

wherein n2 represents an integer of 1 to 5, and A is as defined above.

In general formulas (3a) and (3b), A is preferably —SO₃M or —COOM, and Mis preferably H, a metal atom, NR⁷ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent. R⁷ represents H or an organic group.

In the general formula (3a), n1 is preferably an integer of 5 or less,and more preferably an integer of 2 or less. A is preferably —COOM, andM is preferably H or NH₄.

Examples of the monomer represented by the general formula (3a) includeCF₂═CFCF₂COOM, wherein, M is as defined above).

In the general formula (3b), n2 is preferably an integer of 3 or lessfrom the viewpoint of dispersion stability of the resulting composition,A is preferably —COOM, and M is preferably H or NH₄.

Next, a suitable configuration wherein m is 2 or more in the generalformula (I) will now be described.

The polymer (I) is also preferably a polymer (4) containing apolymerization unit (4) based on at least one monomer selected from thegroup consisting of monomers represented by general formulas (4a) and(4b):

CF₂═CF—CF₂—O-Q^(F1)-CF(-Q^(F2)-CZ¹Z²-A)₂  (4a)

wherein Z¹, Z², and A are as defined above, and Q^(F1) and Q^(F2) arethe same or different and are a single bond, a fluorine-containingalkylene group optionally containing an ether bond between carbon atoms,or a fluorine-containing oxyalkylene group optionally containing anether bond between carbon atoms; and

CF₂═CF—O-Q^(F)-CF(-Q^(F2)-CZ¹Z²-A)₂  (4b)

wherein Z¹, Z², A, Q^(F1), and Q^(F2) are as defined above.

Examples of the monomers represented by the general formulas (4a) and(4b) include:

The polymer (I) is preferably at least one selected from the groupconsisting of the polymer (1), the polymer (2), and the polymer (3), andthe polymer (1) is more preferable.

The polymer (I) may be a homopolymer composed solely of thepolymerization unit (I), or may be a copolymer containing thepolymerization unit (I) and a polymerization unit based on a furthermonomer copolymerizable with the monomer represented by the generalformula (I). From the viewpoint of solubility in a polymerizationmedium, a homopolymer composed solely of the polymerization unit (I) ispreferable. The polymerization unit (I) may be the same or different ateach occurrence, and may contain the polymerization unit (I) based ontwo or more different monomers represented by the general formula (I).

The further monomer is preferably a fluorine-containing ethylenicmonomer having 2 or 3 carbon atoms, such as CF₂═CF₂, CF₂═CFCl, CH₂═CF₂,CFH═CH₂, CFH═CF₂, CF₂═CFCF₃, CH₂═CFCF₃, CH₂═CHCF₃, CHF═CHCF₃ (E-form),and CHF═CHCF₃ (Z-form).

Among these, from the viewpoint of good copolymerizability, at least oneselected from the group consisting of tetrafluoroethylene (CF₂═CF₂),chlorotrifluoroethylene (CF₂═CFCl), and vinylidene fluoride (CH₂═CF₂) ispreferable, and tetrafluoroethylene is more preferable. Accordingly, thepolymerization unit based on the further monomer is preferably apolymerization unit based on tetrafluoroethylene. The polymerizationunit based on a further monomer may be the same or different at eachoccurrence, and the polymer (I) may contain a polymerization unit basedon two or more different further monomers.

Examples of the further monomer include a monomer represented by thefollowing formula (n1-2):

wherein X¹ and X² are the same or different and H or F; X³ is H, F, Cl,CH₃, or CF₃; X⁴ and X⁵ are the same or different and H or F; a and c arethe same or different and 0 or 1; and Rf³ is a fluorine-containing alkylgroup having 1 to 40 carbon atoms or a fluorine-containing alkyl grouphaving 2 to 100 carbon atoms and having an ether bond.

Specifically, preferable examples include CH₂═CFCF₂—O—Rf³, CF₂═CF—O—Rf³,CF₂═CFCF₂—O—Rf³, CF₂═CF—Rf³, CH₂═CH—Rf³, and CH₂═CH—O—Rf³

(wherein Rf³ is as in the above formula (n1-2)).

Examples of the further monomer also include a fluorine-containingacrylate monomer represented by formula (n2-1):

wherein X⁹ is H, F, or CH₃; and Rf⁴ is a fluorine-containing alkyl grouphaving 1 to 40 carbon atoms or a fluorine-containing alkyl group having2 to 100 carbon atoms and having an ether bond. Examples of the Rf⁴group include

—(CH₂

_(d1)

CF₂

_(e1)Z*

wherein Z⁸ is H, F, or Cl; d1 is an integer of 1 to 4; and e1 is aninteger of 1 to 10,

wherein e2 is an integer of 1 to 5,

wherein d3 is an integer of 1 to 4; and e3 is an integer of 1 to 10.

Examples of the further monomer also include a fluorine-containing vinylether represented by formula (n2-2):

CH₂═CHO—Rf⁵  (n2-2)

wherein Rf⁵ is a fluorine-containing alkyl group having 1 to 40 carbonatoms or a fluorine-containing alkyl group having 2 to 100 carbon atomsand having an ether bond.

Specifically, preferable examples of the monomer represented by formula(n2-2) include:

More specific examples thereof include:

and the like.

In addition, examples also include a fluorine-containing allyl etherrepresented by formula (n2-3):

CH₂═CHCH₂O—Rf⁶  (n2-3)

wherein Rf⁶ is a fluorine-containing alkyl group having 1 to 40 carbonatoms or a fluorine-containing alkyl group having 2 to 100 carbon atomsand having an ether bond; and a fluorine-containing vinyl etherrepresented by formula (n2-4):

CH₂═CH—Rf⁷  (n2-4)

wherein Rf⁷ is a fluorine-containing alkyl group having 1 to 40 carbonatoms or a fluorine-containing alkyl group having 2 to 100 carbon atomsand having an ether bond.

Specific examples of monomers represented by formulas (n2-3) and (n2-4)include monomers such as:

and the like.

The polymer (I) usually has a terminal group. The terminal group is aterminal group generated during polymerization, and a representativeterminal group is independently selected from hydrogen, iodine, bromine,a linear or branched alkyl group, and a linear or branched fluoroalkylgroup, and, additionally, may optionally contain at least one catenaryheteroatom. The alkyl group or fluoroalkyl group preferably has 1 to 20carbon atoms.

These terminal groups are, in general, produced from an initiator or achain transfer agent used to form the polymer (I) or produced during achain transfer reaction.

The content of the polymerization unit (I) in the polymer (I) ispreferably 1.0 mol % or more, more preferably 3.0 mol % or more, stillmore preferably 5.0 mol % or more, further preferably 10 mol % or more,still further preferably 20 mol % or more, and particularly preferably30 mol % or more based on all polymerization units. The content is morepreferably 40 mol % or more, still more preferably 60 mol % or more,further preferably 80 mol % or more, particularly preferably 90 mol % ormore, and still further preferably substantially 100 mol %. Mostpreferably, the polymer (I) is composed solely of the polymerizationunit (I).

In the polymer (I), the content of a polymerization unit based on thefurther monomer copolymerizable with the monomer represented by thegeneral formula (I) is preferably 99.0 mol % or less, more preferably97.0 mol % or less, still more preferably 95.0 mol % or less, furtherpreferably 90 mol % or less, and still further preferably 80 mol % orless based on all polymerization units. Further, in the polymer (I), thecontent of a polymerization unit based on the further monomercopolymerizable with the monomer represented by the general formula (I)is preferably 70 mol % or less, more preferably 60 mol % or less, stillmore preferably 40 mol % or less, further preferably 20 mol % or more,particularly preferably 10 mol % or more, and still further preferablysubstantially 0 mol % based on all polymerization units. Veryparticularly preferably, the polymer (I) does not contain apolymerization unit based on the further monomer.

The number average molecular weight of the polymer (I) is preferably0.1×10⁴ or more, more preferably 0.2×10⁴ or more, still more preferably0.3×10⁴ or more, further preferably 0.4×10⁴ or more, still furtherpreferably 0.5×10⁴ or more, particularly preferably 1.0×10⁴ or more, andmost preferably 3.0×10⁴ or more. The number average molecular weight ofthe polymer (I) is also preferably 3.1×10⁴ or more. Further, the numberaverage molecular weight is preferably 750,000 or less, more preferably500,000 or less, still more preferably 400,000 or less, furtherpreferably 300,000 or less, and particularly preferably 200,000 or less.An excessively low number average molecular weight may result ininsufficient stability of an aqueous solution. When the number averagemolecular weight is excessively high, the polymer (I) may partiallyundergo sedimentation, precipitation, or whitening due to storage oraddition of other additives.

The number average molecular weight, and the weight average molecularweight which will be described below, are molecular weight valuescalculated by gel permeation chromatography (GPC) using monodispersepolystyrene as a standard. Further, when measurement by GPC is notpossible, the number average molecular weight of the polymer (1) can bedetermined by the correlation between the number average molecularweight calculated from the number of terminal groups obtained by NMR,FT-IR, or the like, and the melt flow rate. The melt flow rate can bemeasured in accordance with JIS K 7210.

The weight average molecular weight of the polymer (I) is preferably0.2×10⁴ or more, more preferably 0.4×10⁴ or more, still more preferably0.6×10⁴ or more, further preferably 0.8×10⁴ or more, and still furtherpreferably 1.0×10⁴ or more. The weight average molecular weight of thepolymer (I) is also preferably 5.0×10⁴ or more, 10.0×10⁴ or more,15.0×10⁴ or more, 20.0×10⁴ or more, or 25.0×10⁴ or more. Further, theweight average molecular weight of the polymer (I) is preferably150.0×10⁴ or less, more preferably 100.0×10⁴ or less, still morepreferably 60.0×10⁴ or less, further preferably 50.0×10⁴ or less, andparticularly preferably 40.0×10⁴ or less.

The polymer (I) preferably has an ion exchange rate (IXR) of 53 or less.The IXR is defined as the number of carbon atoms in the polymer backbonerelative to the ionic group. A precursor group that becomes ionic byhydrolysis (such as —SO₂F) is not regarded as an ionic group for thepurpose of determining the IXR.

The IXR is preferably 0.5 or more, more preferably 1 or more, still morepreferably 3 or more, further preferably 4 or more, still furtherpreferably 5 or more, and particularly preferably 8 or more. Further,the IXR is more preferably 43 or less, still more preferably 33 or less,and particularly preferably 23 or less.

The ion exchange capacity of the polymer (I) is 0.80 meg/g or more, 1.50meg/g or more, 1.75 meg/g or more, 2.00 meg/g or more, 2.50 meg/g ormore, 2.60 meg/g or more, 3.00 meg/g or more, and 3.50 meg/g or more inthe order of preference. The ion exchange capacity is the content ofionic groups (anionic groups) in the polymer (I) and can be calculatedfrom the composition of the polymer (I).

In the polymer (I), the ionic groups (anionic groups) are typicallydistributed along the polymer backbone. The polymer (I) contains thepolymer backbone together with a repeating side chain bonded to thisbackbone, and this side chain preferably has an ionic group.

The polymer (I) preferably contains an ionic group having a pKa of lessthan 10, more preferably less than 7. The ionic group of the polymer (I)is preferably selected from the group consisting of sulfonate,carboxylate, phosphonate, and phosphate.

The terms “sulfonate, carboxylate, phosphonate, and phosphate” areintended to refer to the respective salts or the respective acids thatcan form salts. A salt when used is preferably an alkali metal salt oran ammonium salt. A preferable ionic group is a sulfonate group.

The polymer (I) preferably has water-solubility. Water-solubility meansthe property of being readily dissolved or dispersed in an aqueousmedium. The particle size of a water-soluble polymer (I) cannot bemeasured by, for example, dynamic light scattering (DLS). On the otherhand, the particle size of a non-water-soluble polymer (I) can bemeasured by, for example, dynamic light scattering (DLS).

The polymer (I) can be produced by a conventionally known method exceptthat the above-described monomer is used.

Further, the polymer (I) may have a content of a dimer and a trimer ofthe monomer represented by the general formula (I) (hereinaftersometimes referred to as a monomer (I)) of 1.0% by mass or less based onthe polymer (I).

In other words, the production method of the present disclosure alsopreferably comprises:

polymerizing the monomer (I) represented by the general formula (I) inan aqueous medium to obtain a crude composition containing a polymer ofthe monomer (I);

removing from the crude composition a dimer and a trimer of the monomer(I) contained in the crude composition to obtain the polymer (I) inwhich the content of the dimer and the trimer of the monomer (I) is 1.0%by mass or less relative to the polymer (I); and

polymerizing tetrafluoroethylene and a modifying monomer in an aqueousmedium in the presence of the polymer (I) to obtain modifiedpolytetrafluoroethylene.

The polymer (I) used in the above production method is substantiallyfree from the dimer and the trimer of the monomer (I). The dimer and thetrimer of the monomer (I) are usually generated when polymerizing themonomer (I) to obtain the polymer (I). The content of the dimer and thetrimer in the polymer (I) is 1.0% by mass or less, preferably 0.1% bymass or less, more preferably 0.01% by mass or less, still morepreferably 0.001% by mass, and particularly preferably 0.0001% by massbased on the polymer (I).

The content of the dimer and trimer in the polymer (I) can be determinedby performing gel permeation chromatography (GPC) analysis on thepolymer (I) and calculating the total proportion of the peak areas (areapercentages) of the dimer and the trimer to the total area of all peaksof the chromatogram obtained by the GPC analysis.

Further, when the content of the dimer and the trimer in the polymer (I)is less than 0.5% by mass based on the polymer (I), the content can bedetermined by liquid chromatography-mass spectrometry (LC/MS/MS)measurement.

Specifically, an aqueous solution having five or more content levels ofthe monomer (I) is prepared, the LC/MS/MS analysis is performed withrespect to each content, the relationship between a content and an arearelative to that content (the integral value of the peak) is plotted,and a calibration curve of the monomer (I) is created. Moreover,calibration curves of the dimer and the trimer of the monomer (I) arecreated from the calibration curve of the monomer (I).

Methanol is added to the polymer (I) to prepare a mixture, and anextract (supernatant) is recovered from the mixture by centrifugation,and the resulting extract is subjected to the LC/MS/MS analysis.

Then, using the calibration curves, the chromatographic area (theintegral value of peaks) of the dimer and the trimer of the monomer (I)can be converted to the content of the dimer and the trimer.

A polymer dispersion substantially free from the dimer and the trimer ofthe monomer (I) can be produced by using the polymer (I) that issubstantially free from the dimer and the trimer when polymerizing afluoromonomer in an aqueous medium.

The polymer (I) is a polymer containing a polymerization unit (I) basedon the monomer (I). The polymer (I) used in the present disclosure is apolymer in which a dimer (a polymer containing two polymerization units(I)) and a trimer (a polymer containing three polymerization units (I))are substantially removed from the polymer (I) containing two or morepolymerization units (I).

The molecular weight of the monomer (I) is preferably 400 or less. Inother words, the polymer (I) is preferably substantially free from adimer and a trimer having a molecular weight of 1200 or less.

The dimer and the trimer of the polymer (I) may be a polymer formed of,as the monomer (I) represented by the general formula (I), one monomer(I) or may be a copolymer formed of two or more monomers (I) havingdifferent structures.

Polymerization of the monomer (I) can be carried out by a known method.By producing a crude composition by such a method, a crude compositionin which the polymer (I) is dispersed or dissolved in an aqueous mediumcan be obtained.

Polymerization of the monomer (I) is preferably carried outsubstantially in the absence of a fluorine-containing surfactant(provided that the monomer (I) represented by the general formula (I) isexcluded). The expression “substantially in the absence of afluorine-containing surfactant” as used herein means that the amount ofthe fluorine-containing surfactant is 10 mass ppm or less based on theaqueous medium. The amount of the fluorine-containing surfactant ispreferably 1 mass ppm or less, more preferably 100 mass ppb or less,still more preferably 10 mass ppb or less, and further preferably 1 massppb or less based on the aqueous medium.

The fluorine-containing surfactant will be described below in thedescription concerning the polymerization of TFE.

The crude composition thus obtained usually contains, as a polymer ofthe monomer (I), the dimer and the trimer in a total amount of more than1.0% by mass based on the mass of the polymer of the monomer (I). Thecontent of the dimer and the trimer in the polymer of the monomer (I),for example, may be 2.0% by mass or more, may be 3.0% by mass or more,may be 30.0% by mass or less, and may be 20.0% by mass or less based onthe polymer of the monomer (I). The content of the dimer and trimer inthe crude composition can be determined by performing a gel permeationchromatography (GPC) analysis on the crude composition and calculatingthe total proportion of the peak areas (area percentages) of the dimerand the trimer to the total area of all peaks of the chromatogramobtained by the GPC analysis.

Next, the dimer and the trimer of the monomer (I) contained in the crudecomposition obtained by the polymerization of the monomer (I) areremoved from the crude composition. The means for removing the dimer andthe trimer is not limited, and is preferably at least one means selectedfrom the group consisting of ultrafiltration, microfiltration, anddialysis membrane treatment, more preferably at least one means selectedfrom the group consisting of microfiltration and dialysis membranetreatment, and still more preferably ultrafiltration.

Previously, it was not known that the polymerization of the monomer (I)produces a dimer and a trimer of the monomer (I) and, as a result, thedimer and the trimer of the monomer (I) are contained in the polymer(I). The mechanism by which the dimer and the trimer of the monomer (I)are produced is not necessarily clear, but it is conjectured that by thepolymerization reaction in the polymerization system which is composedmostly of the monomer (I) among the monomers present in thepolymerization system in particular, dimerization and trimerization ofthe monomer (I) occurs with non-negligible frequency. The presence ofthe dimer and the trimer of the monomer (I) in the polymer (I) wasdiscovered for the first time in the present disclosure, and it wasfound for the first time that the dimer and the trimer of the monomer(I) in the polymer (I) can be highly efficiently removed from thepolymer (I) (a crude composition) by at least one means selected fromthe group consisting of ultrafiltration, microfiltration, and dialysismembrane treatment.

When removing the dimer and the trimer, usually the unreacted monomer(I) is also removed from the crude composition at the same time. Theunreacted monomer (I) even when incorporated into PTFE by polymerizationdoes not necessarily adversely affect the function of PTFE, and thus theunreacted monomer (I) does not necessarily need to be removed. However,removing the unreacted monomer (I) simultaneously with the dimer and thetrimer has the advantage that the amount of monomer to be polymerizedcan be calculated without considering the presence of the unreactedmonomer (I), and PTFE having a desired monomer composition can bereadily produced. Even when the monomer (I) remains in the polymer (I),or even when the monomer (I) is newly added as a co-monomer, dependingon the polymerization reaction in a polymerization system composedmostly of a fluoromonomer (excluding the monomer (I)) among the monomerspresent in the polymerization system, dimerization and trimerization ofthe monomer (I) barely proceed, and the dimer and the trimer of themonomer (I) barely remain in the resulting PTFE.

The crude composition obtained by the polymerization of the monomer (I)may be a composition directly obtained from polymerization, may be whatis obtained after diluting or concentrating a composition directlyobtained from polymerization, or may be what is obtained afterdispersion stabilization treatment or the like. In order to facilitateultrafiltration, microfiltration, or dialysis membrane treatment, it isalso preferable to adjust the viscosity of the crude composition bythese treatments.

The content of the polymer of the monomer (I) in the crude compositionis not limited, and may be, for example, 0.1 to 20% by mass. The contentof the polymer of the monomer (I) in the crude composition is, from theviewpoint of the removal efficiency of the dimer and the trimer,preferably 18.0% by mass or less, more preferably 15.0% by mass or less,still more preferably 12.0% by mass or less, particularly preferably10.0% by mass or less, preferably 0.5% by mass or more, more preferably1.0% by mass or more, still more preferably 1.2% by mass or more, andparticularly preferably 1.5% by mass or more. The content of the polymerof the monomer (I) in the crude composition can be adjusted by, forexample, a method involving adding water to the crude compositionobtained by the polymerization of the monomer (I), or a method involvingconcentrating the crude composition obtained by the polymerization ofthe monomer (I).

The pH of the crude composition is preferably 0 to 11, more preferably0.5 to 8.0, and still more preferably 1.0 to 7.0. The pH of the crudecomposition can be adjusted by adding a pH adjuster to the crudecomposition obtained by the polymerization of the monomer (I). The pHadjuster may be an acid or an alkali, such as a phosphoric acid salt,sodium hydroxide, potassium hydroxide, or aqueous ammonia.

The viscosity of the crude composition is preferably 25 mPa·s or lessbecause ultrafiltration, microfiltration, or dialysis membrane treatmentis facilitated. The viscosity of the crude composition can be adjustedby, for example, a method involving adjusting the number averagemolecular weight of the polymer of the monomer (I), a method involvingadjusting the concentration of the polymer of the monomer (I) in thecrude composition, or a method involving adjusting the temperature ofthe crude composition.

The ultrafiltration or microfiltration is not limited and may beperformed by a cross-flow method or a dead-end method, but a cross-flowmethod is preferable from the viewpoint of reducing the clogging of amembrane.

The ultrafiltration can be performed using an ultrafiltration membrane.Ultrafiltration can be performed using, for example, an ultrafiltrationapparatus having an ultrafiltration membrane, and a centrifugalultrafiltration method, a batch-type ultrafiltration method, acirculation-type ultrafiltration method, and the like can be employed.

The molecular weight cut-off of the ultrafiltration membrane is usuallyabout 0.1×10⁴ to 30×10⁴ Da. The molecular weight cut-off of theultrafiltration membrane is preferably 1.5×10⁴ Da or more because theclogging of the membrane can be suppressed and the dimer and the trimercan be efficiently reduced. The molecular weight cut-off is morepreferably 2.0×10⁴ Da or more, particularly preferably 3.0×10⁴ Da ormore, and most preferably 5.0×10⁴ Da or more. The molecular weightcut-off may be 8.0×10⁴ Da or more. Further, from the viewpoint of theremoval efficiency of the dimer and the trimer, the molecular weightcut-off is preferably 20×10⁴ Da or less, and more preferably 10×10⁴ Daor less.

The molecular weight cut-off of the ultrafiltration membrane can be, forexample, a molecular weight at which 90% of polystyrene having a knownweight average molecular weight that is attempted to pass through themembrane is blocked. The quantification of polystyrene can be performedusing gel permeation chromatography.

The ultrafiltration membrane is not limited and may be in aconventionally known form, and examples include a hollow fiber type, aflat membrane type, a spiral type, and a tubular type. From theviewpoint of suppressing clogging, a hollow fiber type is preferable.

The inner diameter of the hollow fiber type ultrafiltration membrane isnot limited, and may be, for example, 0.1 to 2 mm, and is preferably 0.8to 1.4 mm.

The length of the hollow fiber type ultrafiltration membrane is notlimited, and may be, for example, 0.05 to 3 m, and is preferably 0.05 to2 m.

The material of the ultrafiltration membrane is not limited, andexamples include organic materials such as cellulose, cellulose ester,polysulfone, sulfonated polysulfone, polyethersulfone, sulfonatedpolyether sulfone, chlorinated polyethylene, polypropylene, polyolefin,polyvinyl alcohol, polymethylmethacrylate, polyacrylonitrile,polyvinylidene fluoride, and polytetrafluoroethylene, metals such asstainless steel, and inorganic materials such as ceramics.

The material of the ultrafiltration membrane is preferably an organicmaterial, more preferably chlorinated polyethylene, polypropylene,polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile,polysulfone, or polyethersulfone, and still more preferablypolyacrylonitrile or polyvinylidene fluoride.

Specific examples of the ultrafiltration membrane include G-5 type, G-10type, G-20 type, G-50 type, PW type, and HWS UF type of DESAL; HFM-180,HFM-183, HFM-251, HFM-300, HFM-116, HFM-183, HFM-300, HFK-131, HFK-328,MPT-U20, MPS-U20P, and MPS-U20S of KOCH; SPE1, SPE3, SPE5, SPE10, SPE30,SPV5, SPV50, and SOW30 of Synder; Microza® UF series manufactured byAsahi Kasei Corporation; and NTR 7410 manufactured by Nitto DenkoCorporation.

From the viewpoint of the removal efficiency of the dimer and thetrimer, the ultrafiltration is preferably performed at a pressure of0.01 MPa or more. More preferably, the pressure is 0.03 MPa or more, andstill more preferably 0.05 MPa or more. Further, from the viewpoint ofpressure resistance, the pressure is preferably 0.5 MPa or less, morepreferably 0.25 MPa or less, and still more preferably 0.2 MPa or less.

From the viewpoint of the removal efficiency of the dimer and thetrimer, the ultrafiltration is preferably performed at a flow rate of 10mL/min or more and more preferably performed at a flow rate of 50 mL/minor more, and is preferably performed at a flow rate of 5,000 mL/min orless and more preferably performed at a flow rate of 1,000 mL/min orless.

The microfiltration can be performed using a microfiltration membrane.The microfiltration membrane usually has an average pore size of 0.05 to1.0 μm.

The microfiltration membrane preferably has an average pore size of 0.1μm or more because the dimer and the trimer can be efficiently removed.The average pore size is more preferably 0.075 μm or more, and stillmore preferably 0.1 μm or more. Further, the average pore size ispreferably 1.00 μm or less. The average pore size is more preferably0.50 μm or less, and still more preferably 0.25 μm or less.

The average pore size of the microfiltration membrane can be measured inaccordance with ASTM F₃₁₆₀₃ (bubble point method).

The microfiltration membrane is not limited and may be in aconventionally known form, and examples include a hollow fiber type, aflat membrane type, a spiral type, and a tubular type. From theviewpoint of suppressing clogging, a hollow fiber type is preferable.

The inner diameter of the hollow fiber type ultrafiltration membrane isnot limited, and may be, for example, 0.1 to 2 mm, and is preferably 0.8to 1.4 mm.

The length of the hollow fiber type ultrafiltration membrane is notlimited, and may be, for example, 0.05 to 3 m, and is preferably 0.05 to2 m.

Examples of the material of the microfiltration membrane includecellulose, aromatic polyamide, polyvinyl alcohol, polysulfone, polyethersulfone, polyvinylidene fluoride, polyethylene, polyacrylonitrile,polypropylene, polycarbonate, polytetrafluoroethylene, ceramics, andmetal. Among these, aromatic polyamide, polyvinyl alcohol, polysulfone,polyvinylidene fluoride, polyethylene, polyacrylonitrile, polypropylene,polycarbonate, or polytetrafluoroethylene is preferable, andpolyacrylonitrile or polyvinylidene fluoride is particularly preferable.

Specific examples of the microfiltration membrane include Cefiltmanufactured by NGK Insulators, Ltd.; Microza U Series and Microza PSeries manufactured by Asahi Kasei Corporation; Poreflon SPMW, PoreflonOPMW, and Poreflon PM manufactured by Sumitomo Electric Industries,Ltd.; Trayfil manufactured by Toray Industries, Inc.; NADIR MPO05 andNADIR MV020 manufactured by Microdyn-Nadir; and X-Flow manufactured byNorit.

From the viewpoint of the removal efficiency of the dimer and thetrimer, the microfiltration is preferably performed at a pressure of0.01 MPa or more. The pressure is more preferably 0.03 MPa or more, andstill more preferably 0.05 MPa or more. Further, from the viewpoint ofpressure resistance, the pressure is preferably 0.5 MPa or less, morepreferably 0.25 MPa or less, and still more preferably 0.2 MPa or less.

From the viewpoint of the removal efficiency of the dimer and thetrimer, the microfiltration is preferably performed at a flow rate of 10mL/min or more and more preferably performed at a flow rate of 50 mL/minor more, and is preferably performed at a flow rate of 5,000 mL/min orless and more preferably performed at a flow rate of 1,000 mL/min orless.

The dialysis membrane treatment is performed using a dialysis membrane.The dialysis membrane usually has a molecular weight cut-off of 0.05×10⁴to 100×10⁴ Da.

The molecular weight cut-off of the dialysis membrane is preferably0.3×10⁴ Da or more because the clogging of the membrane can besuppressed and the dimer and the trimer can be efficiently removed. Themolecular weight cut-off is more preferably 0.5×10⁴ Da or more, stillmore preferably 1.0×10⁴ Da or more, further preferably 1.5×10⁴ Da ormore, still further preferably 2.0×10⁴ Da or more, particularlypreferably 3.0×10⁴ Da or more, and most preferably 5.0×10⁴ Da or more.The molecular weight cut-off may be 8.0×10⁴ Da or more.

Further, from the viewpoint of the removal efficiency of the dimer andthe trimer, the molecular weight cut-off is preferably 20×10⁴ Da orless, and more preferably 10×10⁴ Da or less.

The molecular weight cut-off of the dialysis membrane can be measuredby, for example, the same method as the ultrafiltration membrane.

The material of the dialysis membrane is not limited, and examplesinclude cellulose, polyacrylonitrile, polymethylmethacrylate, ethylenevinyl alcohol copolymers, polysulfone, polyamide, and polyester polymeralloy.

Specific examples of the dialysis membrane include Spectra/Por®Float-A-Lyzer, Tube-A-Lyzer, Dialysis tubing, 6 Diarysis tubing, and 7Diarysis tubing manufactured by Spectrum Laboratories Inc.

Ultrafiltration, microfiltration, or dialysis membrane treatment ispreferably performed at a temperature of 10° C. or higher. Thetemperature is more preferably 15° C. or higher, still more preferably20° C. or higher, and particularly preferably 30° C. or higher. Byadjusting the temperature within the above range, the dimer and thetrimer can be more efficiently reduced. The temperature is preferably90° C. or lower, more preferably 80° C. or lower, still more preferably70° C. or lower, and particularly preferably 60° C. or lower.

Ultrafiltration, microfiltration, or dialysis membrane treatment can beperformed while adding water to the crude composition or adjusting thepH of the crude composition. Water may be added intermittently to thecrude composition or continuously added to the crude composition.

The end point of ultrafiltration, microfiltration, or dialysis membranetreatment is suitably determined, and is not limited. Further, in theultrafiltration, microfiltration, or dialysis membrane treatment, inorder to improve the durability of the filtration membrane, the membranemay be backwashed once per a filtration time of 1 to 24 hours as a roughguide.

By removing the dimer and the trimer of the monomer (I) from the crudecomposition containing the polymer of the monomer (I), an aqueoussolution containing the polymer (I) substantially free from the dimerand the trimer is usually obtained. The polymer (I) used in theproduction method may be the polymer (I) contained in the obtainedaqueous solution, or may be the polymer (I) obtained by being separatedfrom the aqueous solution. The method for separating the polymer (I)from the aqueous solution is not limited. For example, the polymer (I)can be separated by a method such as coagulation, washing, or drying ofthe polymer (I) in the aqueous solution.

The polymer (I) may be an aqueous solution containing the polymer (I). Apreferable content of the dimer and the trimer of the monomer (I) basedon the polymer (I) in the aqueous solution is the same as the content ofthe dimer and the trimer in the polymer (1).

In the production method of the present disclosure, two or more polymers(I) may be used at the same time.

The production method of the present disclosure comprises polymerizingtetrafluoroethylene and a modifying monomer in an aqueous medium in thepresence of the monomer (I) to obtain modified polytetrafluoroethylene.PTFE obtained by polymerizing TFE in an aqueous medium is usuallyobtained in the form of primary particles dispersed in the aqueousdispersion.

In the polymerization step, the polymerization temperature and thepolymerization pressure are suitably determined in accordance with thetypes of the monomers used, the molecular weight of the target modifiedPTFE, and the reaction rate.

For example, the polymerization temperature is preferably 10 to 150° C.The polymerization temperature is more preferably 30° C. or higher, andstill more preferably 50° C. or higher. Further, the polymerizationtemperature is more preferably 120° C. or lower, and still morepreferably 100° C. or lower.

The polymerization pressure is preferably 0.05 to 10 MPaG. Thepolymerization pressure is more preferably 0.3 MPaG or higher, and stillmore preferably 0.5 MPaG or higher. The polymerization pressure is morepreferably 5.0 MPaG or lower, and still more preferably 3.0 MPaG orlower. In particular, from the viewpoint of improving the yield of PTFE,the polymerization pressure is preferably 1.0 MPaG or higher, morepreferably 1.2 MPaG or higher, still more preferably 1.5 MPaG or higher,particularly preferably 1.8 MPaG or higher, and most preferably 2.0 MPaGor higher.

The total amount of the modifying monomer added in the polymerizationstep is preferably 0.00001% by mass or more, more preferably 0.0001% bymass or more, still more preferably 0.001% by mass or more, furtherpreferably 0.005% by mass or more, and particularly preferably 0.009% bymass or more based on the obtained modified polytetrafluoroethylene.Further, the total amount of the modifying monomer added duringpolymerization is 1.0% by mass or less, 0.90% by mass or less, 0.50% bymass or less, 0.40% by mass or less, 0.30% by mass or less, 0.20% bymass or less, 0.15% by mass or less, 0.10% by mass or less, and 0.05% bymass or less in the order of preference based on the obtained modifiedPTFE.

In the polymerization step, the amount of the polymer (I) at theinitiation of polymerization is preferably 1 mass ppm or more based onthe aqueous medium. The amount of the polymer (I) at the initiation ofpolymerization is preferably 10 mass ppm or more, more preferably 50mass ppm or more, still more preferably 100 mass ppm or more, andfurther preferably 200 mass ppm or more. The upper limit thereof ispreferably, but not limited to, 100,000 mass ppm, and more preferably50,000 mass ppm, for example. When the amount of the polymer (I) at theinitiation of polymerization is in the above range, it is possible toobtain an aqueous dispersion having a smaller average primary particlesize and superior stability. Also, the aspect ratio of the primaryparticles can be made smaller.

It can be said that the polymerization started when the gasfluoromonomer in the reactor became modified polytetrafluoroethylene andthe pressure drop in the reactor occurred. U.S. Pat. No. 3,391,099(Punderson) discloses a dispersion polymerization of tetrafluoroethylenein an aqueous medium comprising two separate steps of a polymerizationprocess comprising: first the formation of a polymer nucleus as anucleation site, and then the growth step comprising polymerization ofthe established particles. The polymerization is usually started whenboth the monomer to be polymerized and the polymerization initiator arecharged in the reactor. Further, in the present disclosure, an additiverelated to the formation of a nucleation site is referred to as anucleating agent.

The total amount of the polymer (I) added is preferably 0.0001 to 15% bymass based on 100% by mass of the aqueous medium. The lower limitthereof is more preferably 0.001% by mass, while the upper limit thereofis more preferably 1% by mass. Less than 0.0001% by mass of the polymer(I) may cause insufficient dispersibility. More than 15% by mass of thepolymer (I) may fail to give the effects corresponding to its amount.The amount of the polymer (I) added is appropriately determineddepending on the type of monomer used, the molecular weight of thetarget modified PTFE, and the like.

The polymerization step is the step of polymerizing tetrafluoroethyleneand a modifying monomer in an aqueous medium in the presence of thepolymer (I), and the step also preferably includes continuously addingthe polymer (I).

Adding the polymer (I) continuously means, for example, adding thepolymer (I) not all at once, but adding over time and withoutinterruption or adding in portions.

By including the above step, or in other words, by continuously addingthe polymer (I), it is possible to obtain an aqueous dispersion having asmaller average primary particle size and superior stability. Also, theaspect ratio of the primary particles can be made smaller.

In the step of continuously adding the polymer (I), the amount of thepolymer (I) added is preferably 0.001 to 10% by mass based on 100% bymass of the aqueous medium. The lower limit thereof is more preferably0.005% by mass, still more preferably 0.01% by mass while the upperlimit thereof is more preferably 5% by mass, still more preferably 2% bymass.

The production method of the present disclosure preferably furtherincludes the step of adding a modifying monomer before the initiation ofpolymerization or when the concentration of particles of modified PTFEformed in the aqueous medium is 10.0% by mass or less, preferably 5.0%by mass or less. The modifying monomer is usually added to a reactor.

By adding the modifying monomer at the initial stage of polymerization,an aqueous dispersion having a small average primary particle size, asmall aspect ratio of the primary particles, and excellent stability canbe obtained.

The modifying monomer may be added before the initiation of thepolymerization, may be added at the same time as the initiation of thepolymerization, or may be added during the period in which the nuclei ofmodified PTFE particles are formed after polymerization is initiated.The modifying monomer is added at least before the initiation ofpolymerization or when the concentration of particles of modified PTFEformed in the aqueous medium is 10.0% by mass or less, and the modifyingmonomer may be further added when the concentration of particles ofmodified PTFE exceeds 10.0% by mass.

For example, the modifying monomer may be continuously added from thetime when the concentration of particles of modified PTFE is 10.0% bymass or less to any time when the concentration exceeds 10.0% by mass.Further, the modifying monomer may be added at least once when theconcentration of particles of modified PTFE is 10.0% by mass or less,and the modifying monomer may be added at least once any time when theconcentration exceeds 10.0% by weight. The method of adding themodifying monomer may be pushing the modifying monomer into the reactorby tetrafluoroethylene.

The amount of the modifying monomer added before the initiation ofpolymerization or when the concentration of particles of modified PTFEformed in the aqueous medium is 10.0% by mass or less, preferably 5.0%by mass or less, is 0.00001% by mass or more, preferably 0.0001% by massor more, more preferably 0.001% by mass or more, and still morepreferably 0.003% by mass or more based on the obtained modifiedpolytetrafluoroethylene. Further, the amount of the modifying monomeradded before the initiation of polymerization or when the concentrationof particles of modified PTFE formed in the aqueous medium is 10.0% bymass or less, preferably 5.0% by mass or less, is 1.0% by mass or less,0.90% by mass or less, 0.50% by mass or less, 0.40% by mass or less,0.30% by mass or less, 0.20% by mass or less, 0.15% by mass or less,0.10% by mass or less, and 0.05% by mass or less, in the order ofpreference, based on the resulting modified PTFE.

It is also preferable that the production method of the presentdisclosure further includes the step of adding a polymerizationterminator (a radical scavenger) to the aqueous medium (hereinafter,also referred to as a “polymerization terminator adding step”). In thepolymerization, tetrafluoroethylene and the above-described modifyingmonomer may be polymerized.

The polymerization terminator adding step is performed during thepolymerization step. By adding a polymerization terminator during thepolymerization step, the resulting modified PTFE attains excellentstretchability.

The polymerization terminator may be a compound having no reinitiationability after addition or chain transfer to a free radical in thepolymerization system. Specifically, a compound that readily undergoes achain transfer reaction with a primary radical or propagating radicaland then generates a stable radical that does not react with a monomeror a compound that readily undergoes an addition reaction with a primaryradical or propagating radical to generate a stable radical is used.

The activity of what is commonly referred to as a chain transfer agentis characterized by the chain transfer constant and the reinitiationefficiency, but among the chain transfer agents, those having almost 0%reinitiation efficiency are called polymerization terminators.

The polymerization terminator in the present disclosure is preferably atleast one selected from the group consisting of aromatic hydroxycompounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds,terpenes, thiocyanates, and cupric chloride (CuCl₂).

Examples of the aromatic hydroxy compound include unsubstituted phenols,polyhydric phenols, salicylic acid, m- or p-salicylic acid, gallic acid,and naphthol.

Examples of the unsubstituted phenol include o-, m-, or p-nitrophenol,o-, m-, or p-aminophenol, and p-nitrosophenol.

Examples of the polyhydric phenol include catechol, resorcin,hydroquinone, pyrogallol, phloroglucin, and naphthresorcinol.

Examples of the aromatic amines include o-, m-, or p-phenylenediamineand benzidine.

Examples of the quinone compound include hydroquinone, o-, m- orp-benzoquinone, 1,4-naphthoquinone, and alizarin.

Examples of the thiocyanate include anonium thiocyanate (NH₄SCN),potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN).

In particular, the polymerization terminator is preferably a quinonecompound, and more preferably hydroquinone.

From the viewpoint of reducing the standard specific gravity, thepolymerization terminator is preferably added before 90% by mass of alltetrafluoroethylene consumed in the polymerization reaction ispolymerized. More preferably, the polymerization terminator is addedbefore 85% by mass, and still more preferably 85% by mass, of alltetrafluoroethylene consumed in the polymerization reaction ispolymerized.

Further, the polymerization terminator is preferably added after 5% bymass of all tetrafluoroethylene consumed in the polymerization reactionis polymerized, and more preferably after 10% by mass is polymerized.The amount of the polymerization terminator added is preferably anamount corresponding to 0.1 to 20% by mass ppm and more preferably anamount corresponding to 3 to 10% by mass ppm of the mass of the aqueousmedium used.

It is also preferable that the production method further includes thestep of adding a decomposer to the aqueous medium. By adding thedecomposer, the concentration of a radical during polymerization can beadjusted.

Examples of the decomposer include sulfite, bisulfite, bromate, diimine,oxalic acid, copper salts, and iron salts. Examples of the sulfiteinclude sodium sulfite and ammonium sulfite. An example of the coppersalt is copper(II) sulfate and an example of the iron salt is iron(II)sulfate.

The amount of the decomposer added is in the range of 25 to 300% by massbased on the amount of the oxidizing agent combined as a polymerizationinitiator (redox initiator described later). The amount thereof ispreferably 25 to 150% by mass, and more preferably 50 to 100% by mass.

Further, the decomposer is preferably added after 5% by mass of alltetrafluoroethylene consumed in the polymerization reaction ispolymerized, and more preferably after 10% by mass is polymerized. Theamount of the decomposer added is preferably an amount corresponding to0.1 to 20% by mass ppm and more preferably an amount corresponding to 3to 10% by mass ppm of the mass of the aqueous medium used.

The method for producing modified PTFE of the present disclosure can beefficiently performed by using at least one polymer (I). The modifiedPTFE of the present disclosure may be produced by simultaneously usingtwo or more polymers (I), or may be produced by simultaneously using asurfactant, as long as the compound has volatility or may remain in amolded body or the like made of modified PTFE.

The polymerization step may further polymerize tetrafluoroethylene and amodifying monomer in the presence of a nucleating agent.

In the polymerization, the nucleating agent is preferably added to theaqueous medium before the initiation of the polymerization reaction orbefore the concentration of PTFE in the aqueous dispersion reaches 5.0%by mass as the polymerization reaction proceeds. By adding a nucleatingagent at the initial stage of polymerization, more particles can begenerated during polymerization, and primary particles having a smalleraverage primary particle size and aspect ratio can be obtained. That is,the nucleating agent may be added before the initiation of thepolymerization, may be added at the same time as the initiation of thepolymerization, or may be added during the period in which the nuclei ofPTFE particles are formed after polymerization is initiated.

The time when the nucleating agent is added is before the initiation ofpolymerization or before the concentration of PTFE in the aqueousdispersion reaches 5.0% by mass as the polymerization reaction proceeds,preferably before the initiation of polymerization or before theconcentration of PTFE reaches 3.0% by mass, more preferably before theinitiation of polymerization or before the concentration of PTFE reaches1.0% by mass, still more preferably before the initiation ofpolymerization or before the concentration of PTFE reaches 0.5% by mass,and particularly preferably before the initiation of polymerization orat the same time as the initiation of polymerization.

The amount of the nucleating agent added is preferably 0.001 to 0.1 massppm based on the aqueous medium because more particles can be generatedduring polymerization, and primary particles having a smaller averageprimary particle size and aspect ratio can be obtained. The lower limitof the amount of the nucleating agent is 0.01 mass ppm, 0.05 mass ppm,and 0.1 mass ppm in the order of preference. The upper limit of theamount of the nucleating agent is 2000 mass ppm, 1000 mass ppm, 500 massppm, 100 mass ppm, 50 mass ppm, and 10 mass ppm in the order ofpreference.

The nucleating agent is preferably at least one selected from the groupconsisting of, for example, fluoropolyether, nonionic surfactant, andchain transfer agent.

In this case, the polymerization step is preferably the step ofpolymerizing tetrafluoroethylene and a modifying monomer in an aqueousmedium in the presence of the polymer (I) and the nucleating agent toobtain modified PTFE.

The nucleating agent is more preferably a chain transfer agent and stillmore preferably a chain transfer agent and one or both of a nonionicsurfactant and fluoropolyether because more particles can be generatedduring polymerization, and primary particles having a smaller averageprimary particle size and aspect ratio can be obtained. When a chaintransfer agent and one or both of a nonionic surfactant andfluoropolyether are used as the nucleating agent, the nucleating agentcontains a combination of a chain transfer agent and a nonionicsurfactant, a combination of a chain transfer agent and fluoropolyether,or a combination of a chain transfer agent, a nonionic surfactant, andfluoropolyether. In particular, the nucleating agent is preferably acombination of a chain transfer agent and a nonionic surfactant.

The fluoropolyether is preferably perfluoropolyether. Thefluoropolyether itself provides a polymerization field and can be anucleation site.

The fluoropolyether preferably has a repeating unit represented by theformulas (1a) to (1d):

(—CFCF₃—CF₂—O—)_(n)  (1a)

(—CF₂—CF₂—CF₂—O—)_(n)  (1b)

(—CF₂—CF₂—O—)_(n)—(—CF₂—O—)_(m)  (1c)

(—CF₂—CFCF₃—O—)_(n)—(—CF₂—O—)_(m)  (1d)

wherein m and n are integers of 1 or more.

The fluoropolyether is preferably fluoropolyetheric acid or a saltthereof, and the fluoropolyetheric acid is preferably a carboxylic acid,a sulfonic acid, a sulfonamide, or a phosphonic acid, and morepreferably a carboxylic acid. Among the fluoropolyetheric acid or a saltthereof, a salt of fluoropolyetheric acid is preferable, an anonium saltof fluoropolyetheric acid is more preferable, and an ammonium salt offluoropolyethercarboxylic acid is still more preferable.

The fluoropolyetheric acid or a salt thereof can have any chainstructure in which oxygen atoms in the main chain of the molecule areseparated by saturated fluorocarbon groups having 1 to 3 carbon atoms.Two or more types of fluorocarbon groups can be present in the molecule.

The fluoropolyether acid or its salt is preferably a compoundrepresented by the following formula:

CF₃—CF₂—CF₂—O(—CFCF₃—CF₂—O—)_(n)CFCF₃—COOH,

CF₃—CF₂—CF₂—O(—CF₂—CF₂—CF₂—O—)_(n)—CF₂—CF₂OOH, or

HOOC—CF₂—O(—CF₂—CF₂—O—)_(n)—(—CF₂—O—)_(m)CF₂COOH,

(wherein m and n are the same as above) or a salt thereof.

These structures are described in J. Appl. Polymer Sci., 57, 797(1995)examined by Kasai. As disclosed herein, such fluoropolyethers can have acarboxylic acid group or a salt thereof at one end or both ends.Similarly, such fluoropolyethers may have a sulfonic acid or phosphonicacid group or a salt thereof at one end or both ends. In addition,fluoropolyethers having acid functional groups at both ends may havedifferent groups at each end. Regarding monofunctional fluoropolyether,the other end of the molecule is usually perfluorinated, but may containa hydrogen or chlorine atom.

Fluoropolyethers having acid groups at one or both ends have at leasttwo ether oxygens, preferably at least four ether oxygens, and stillmore preferably at least six ether oxygens. Preferably, at least onefluorocarbon group separating ether oxygens, more preferably at leasttwo of such fluorocarbon groups, has 2 or 3 carbon atoms. Still morepreferably, at least 50% of the fluorocarbon groups separating etheroxygens has 2 or 3 carbon atoms. Also preferably, the fluoropolyetherhas at least 15 carbon atoms in total, and for example, a preferableminimum value of n or n+m in the repeating unit structure is preferablyat least 5. Two or more fluoropolyethers having an acid group at one endor both ends can be used in the methods according to the presentdisclosure. Typically, fluoropolyethers may contain a plurality ofcompounds in varying proportions within the molecular weight rangerelative to the average molecular weight, unless special care is takenin the production of a single specific fluoropolyether compound.

The fluoropolyether preferably has a number average molecular weight of800 g/mol or more. The fluoropolyether acid or the salt thereofpreferably has a number average molecular weight of less than 6,000g/mol, because the fluoropolyether acid or the salt thereof may bedifficult to disperse in an aqueous medium. The fluoropolyether acid orthe salt thereof more preferably has a number average molecular weightof 800 to 3,500 g/mol, more preferably 900 to 3,500 g/mol, and stillmore preferably 1,000 to 2,500 g/mol.

The amount of the fluoropolyether is preferably 5 to 5,000 mass ppm,more preferably 5 to 3,000 mass ppm, and still more preferably 5 to2,000 mass ppm based on the aqueous medium, a more preferable lowerlimit is 10 mass ppm, 20 mass ppm, 30 mass ppm, and 50 mass ppm in theorder of preference, and a more preferable upper limit is 1,000 massppm, 500 mass ppm, and 100 mass ppm in the order of preference.

Examples of the nonionic surfactant as the nucleating agent ispreferably a fluorine-free nonionic surfactant. Examples includeether-type nonionic surfactants such as polyoxyethylene alkyl phenylether, polyoxyethylene alkyl ether, and polyoxyethylene alkylene alkylether; polyoxyethylene derivatives such as ethylene oxide/propyleneoxide block copolymers; ester-type nonionic surfactants such as sorbitanfatty acid esters, polyoxyethylene sorbitan fatty acid esters,polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters,and polyoxyethylene fatty acid esters; and amine-based nonionicsurfactants such as polyoxyethylene alkyl amine and alkylalkanolamide.

The nonionic surfactant itself provides a polymerization field and,moreover, by chain-transferring a radical at the initial stage, yields alarge amount of a low molecular weight fluoropolymer and thus can be anucleation site.

Examples of the nonionic surfactant include a block copolymer ofpolyethylene glycol-polypropylene glycol-polyethylene glycol.

Examples of commercially available products of the nonionic surfactantinclude Genapol X080 (product name, available from Clariant), NOIGEN TDSseries (available from DKS Co., Ltd.) exemplified by NOIGEN TDS-80(trade name), LEOCOL TD series (available from Lion Corp.) exemplifiedby LEOCOL TD-90 (trade name), LIONOL® TD series (available from LionCorp.), T-Det A series (available from Harcros Chemicals Inc.)exemplified by T-Det A 138 (trade name), and TERGITOL® 15 S series(available from The Dow Chemical Company).

The hydrophobic group of the nonionic surfactant may be any of analkylphenol group, a linear alkyl group, and a branched alkyl group.

Examples of the nonionic surfactant include a compound represented bythe following general formula (i):

R³—O-A¹-H  (i)

wherein R³ is a linear or branched primary or secondary alkyl grouphaving 8 to 18 carbon atoms, and A¹ is a polyoxyalkylene chain. R³preferably has 10 to 16, more preferably 12 to 16 carbon atoms. When R³has 18 or less carbon atoms, the aqueous dispersion tends to have gooddispersion stability. Further, when R³ has more than 18 carbon atoms, itis difficult to handle due to its high flowing temperature. When R³ hasless than 8 carbon atoms, the surface tension of the aqueous dispersionbecomes high, so that the permeability and wettability are likely todecrease.

The polyoxyalkylene chain may be composed of oxyethylene andoxypropylene. The polyoxyalkylene chain is composed of an averagerepeating number of 5 to 20 oxyethylene groups and an average repeatingnumber of 0 to 2 oxypropylene groups, and is a hydrophilic group. Thenumber of oxyethylene units may have either a broad or narrow monomodaldistribution as typically supplied, or a broader or bimodal distributionwhich may be obtained by blending. When the average repeating number ofoxypropylene groups is more than 0, the oxyethylene groups andoxypropylene groups in the polyoxyalkylene chain may be arranged inblocks or randomly.

From the viewpoint of viscosity and stability of the aqueous dispersion,a polyoxyalkylene chain composed of an average repeating number of 7 to12 oxyethylene groups and an average repeating number of 0 to 2oxypropylene groups is preferred. In particular, when A¹ has 0.5 to 1.5oxypropylene groups on average, low foaming properties are good, whichis preferable.

More preferably, R³ is (R′)(R″)HC—, where R′ and R″ are the same ordifferent linear, branched, or cyclic alkyl groups, and the total amountof carbon atoms is at least 5, preferably 7 to 17. Preferably, at leastone of R′ or R″ is a branched or cyclic hydrocarbon group.

Specific examples of the polyoxyethylene alkyl ether includeC₁₃H₂₇—O—(C₂H₄₀)₁₀—H, C₁₂H₂₅—O—(C₂H₄₀)₁₀—H,C₁₀H₂₁CH(CH₃)CH₂—O—(C₂H₄₀)₉—H, C₁₃H₂₇—O—(C₂H₄₀)₉—(CH(CH₃)CH₂O)—H,C₁₆H₃₃—O—(C₂H₄₀)₁₀—H, and HC(CH₁₁)(C₇H₁₅)—O—(C₂H₄₀)₉—H. Examples ofcommercially available products of polyoxyethylene alkyl ether includeGenapol X080 (product name, available from Clariant), NOIGEN TDS series(available from DKS Co., Ltd.) exemplified by NOIGEN TDS-80 (tradename), LEOCOL TD series (available from Lion Corp.) exemplified byLEOCOL TD-90 (trade name), LIONOL® TD series (available from LionCorp.), T-Det A series (available from Harcros Chemicals Inc.)exemplified by T-Det A 138 (trade name), and TERGITOL® 15 S series(available from The Dow Chemical Company).

The nonionic surfactant is preferably an ethoxylate of2,6,8-trimethyl-4-nonanol having about 4 to about 18 ethylene oxideunits on average, an ethoxylate of 2,6,8-trimethyl-4-nonanol havingabout 6 to about 12 ethylene oxide units on average, or a mixturethereof. This type of nonionic surfactant is also commerciallyavailable, for example, as TERGITOL TMN-6, TERGITOL TIMN-10, andTERGITOL TMN-100X (all product names, available from Dow Chemical Co.,Ltd.).

The hydrophobic group of the nonionic surfactant may be any of analkylphenol group, a linear alkyl group, and a branched alkyl group.Examples of the polyoxyethylene alkylphenyl ether-based nonioniccompound include, for example, a compound represented by the followinggeneral formula (ii):

R⁴—C₆H₄—O-A²-H  (ii)

wherein R⁴ is a linear or branched primary or secondary alkyl grouphaving 4 to 12 carbon atoms, and A² is a polyoxyalkylene chain. Specificexamples of the polyoxyethylene alkylphenyl ether-based nonioniccompound include Triton X-100 (trade name, available from Dow ChemicalCo., Ltd.).

Examples of the nonionic surfactant also include polyol compounds.Specific examples thereof include those described in InternationalPublication No. WO2011/014715.

Typical examples of the polyol compound include compounds having one ormore sugar units as polyol unit. The sugar units may have been modifiedto contain at least one long chain. Examples of suitable polyolcompounds containing at least one long chain moiety include alkylglycosides, modified alkyl glycosides, sugar esters, and combinationsthereof. Examples of the sugars include, but are not limited to,monosaccharides, oligosaccharides, and sorbitanes. Examples ofmonosaccharides include pentoses and hexoses. Typical examples ofmonosaccharides include ribose, glucose, galactose, mannose, fructose,arabinose, and xylose. Examples of oligosaccharides include oligomers of2 to 10 of the same or different monosaccharides. Examples ofoligosaccharides include, but are not limited to, saccharose, maltose,lactose, raffinose, and isomaltose.

Typically, sugars suitable for use as the polyol compound include cycliccompounds containing a 5-membered ring of four carbon atoms and oneheteroatom (typically oxygen or sulfur, preferably oxygen atom), orcyclic compounds containing a 6-membered ring of five carbon atoms andone heteroatom as described above, preferably, an oxygen atom. Thesefurther contain at least two or at least three hydroxy groups (—OHgroups) bonded to the carbon ring atoms. Typically, the sugars have beenmodified in that one or more of the hydrogen atoms of a hydroxy group(and/or hydroxyalkyl group) bonded to the carbon ring atoms has beensubstituted by the long chain residues such that an ether or ester bondis created between the long chain residue and the sugar moiety.

The sugar-based polyol may contain a single sugar unit or a plurality ofsugar units. The single sugar unit or the plurality of sugar units maybe modified with long chain moieties as described above. Specificexamples of sugar-based polyol compound include glycosides, sugaresters, sorbitan esters, and mixtures and combinations thereof.

A preferred type of polyol compounds are alkyl or modified alkylglucosides. These type of surfactants contains at least one glucosemoiety. Examples of alkyl or modified alkyl glucosides include compoundsrepresented by the formula:

wherein x represents 0, 1, 2, 3, 4, or 5 and R¹ and R² eachindependently represent H or a long chain unit containing at least 6carbon atoms, with the proviso that at least one of R¹ or R² is not H.Typical examples of R¹ and R² include aliphatic alcohol residues.Examples of the aliphatic alcohols include hexanol, heptanol, octanol,nonanol, decanol, undecanol, dodecanol (lauryl alcohol), tetradecanol,hexadecanol (cetyl alcohol), heptadecanol, octadecanol (stearylalcohol), eicosanoic acid, and combinations thereof.

It is understood that the above formula represents specific examples ofalkyl poly glucosides showing glucose in its pyranose form but othersugars or the same sugars but in different enantiomeric ordiastereomeric forms may also be used.

Alkyl glucosides are available, for example, by acid-catalyzed reactionsof glucose, starch, or n-butyl glucoside with aliphatic alcohols whichtypically yields a mixture of various alkyl glucosides (Alkylpolyglycylside, Rompp, Lexikon Chemie, Version 2.0, Stuttgart/New York,Georg Thieme Verlag, 1999). Examples of the aliphatic alcohols includehexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol(lauryl alcohol), tetradecanol, hexadecanol (cetyl alcohol),heptadecanol, octadecanol (stearyl alcohol), eicosanoic acid, andcombinations thereof. Alkyl glucosides are also commercially availableunder the trade name GLUCOPON or DISPONIL from Cognis GmbH, Dusseldorf,Germany.

Examples of other nonionic surfactants include bifunctional blockcopolymers supplied from BASF as Pluronic® R series, tridecyl alcoholalkoxylates supplied from BASF as Iconol® TDA series, andhydrocarbon-containing siloxane surfactants, preferably hydrocarbonsurfactants. In the sense that the hydrocarbyl groups are fullysubstituted with hydrogen atoms where they can be substituted by halogensuch as fluorine, these siloxane surfactants can also be regarded ashydrocarbon surfactants, i.e. the monovalent substituents on thehydrocarbyl groups are hydrogen.

Examples of nonionic hydrocarbon surfactants are as follows.

Polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether,polyoxyethylene alkyl ester, sorbitan alkyl ester, polyoxyethylenesorbitan alkyl ester, glycerol ester, and derivatives thereof.

Specific examples of polyoxyethylene alkyl ethers: polyoxyethylenelauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearylether, polyoxyethylene oleyl ether, polyoxyethylene biphenyl ether, andthe like.

Specific examples of polyoxyethylene alkyl phenyl ether: polyoxyethylenenonylphenyl ether, polyoxyethylene octylphenyl ether, and the like.

Specific examples of polyoxyethylene alkyl esters: polyethylene glycolmonolaurylate, polyethylene glycol monooleate, polyethylene glycolmonostearate, and the like.

Specific examples of sorbitan alkyl ester: polyoxyethylene sorbitanmonolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylenesorbitan monostearate, polyoxyethylene sorbitan monooleate, and thelike.

Specific examples of polyoxyethylene sorbitan alkyl ester:polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitanmonopalmitate, polyoxyethylene sorbitan monostearate, and the like.

Specific examples of glycerol ester: glycerol monomyristate, glycerolmonostearate, glycerol monooleate, and the like.

Specific examples of the above derivatives: polyoxyethylene alkylamine,polyoxyethylene alkylphenyl-formaldehyde condensate, polyoxyethylenealkyl ether phosphate, and the like.

The ethers and esters may have an HLB value of 10 to 18.

Examples of nonionic surfactants include Triton X series (X15, X45,X100, etc.), Tergitol® 15-S series, and Tergitol® manufactured by DowChemical Company, TMN series (TMN-6, TIMN-10, TMN-100, etc.), Tergitol®L series, Pluronic® R series (31R1, 17R2, 10R5, 25R4 (m to 22, n to 23),and Iconol® TDA series (TDA-6, TDA-9, TDA-10) manufactured by BASF.

The nonionic surfactant is preferably at least one selected from thegroup consisting of a nonionic surfactant represented by the generalformula (i) and a nonionic surfactant represented by the general formula(ii).

The amount of the nonionic surfactant is preferably 0.1 to 0.0000001% bymass, more preferably 0.01 to 0.000001% by mass, based on the aqueousmedium. A more preferable lower limit of the amount of the nonionicsurfactant is 0.000005% by mass and 0.00001% by mass in the order ofpreference. A more preferable upper limit of the amount of the nonionicsurfactant is 0.005% by mass, 0.001% by mass, 0.0005% by mass, and0.0001% by mass in the order of preference.

The chain transfer agent, by chain-transferring a radical at the initialstage, yields a large amount of a low molecular weight fluoropolymer andthus can be a nucleation site.

Examples of the chain transfer agent include esters such as dimethylmalonate, diethyl malonate, methyl acetate, ethyl acetate, butylacetate, and dimethyl succinate, as well as isopentane, methane, ethane,propane, isobutane, methanol, ethanol, isopropanol, acetone, variousmercaptans, various halogenated hydrocarbons such as carbontetrachloride, and cyclohexane.

The chain transfer agent to be used may be a bromine compound or aniodine compound. An example of a polymerization method using a brominecompound or an iodine compound is a method of performing polymerizationof a fluoromonomer in an aqueous medium substantially in the absence ofoxygen and in the presence of a bromine compound or an iodine compound(iodine transfer polymerization). Representative examples of the brominecompound or the iodine compound to be used include compounds representedby the following general formula:

R^(a)I_(x)Br_(y)

wherein x and y are each an integer of 0 to 2 and satisfy 1≤x+y≤2; andR^(a) is a saturated or unsaturated fluorohydrocarbon orchlorofluorohydrocarbon group having 1 to 16 carbon atoms, or ahydrocarbon group having 1 to 3 carbon atoms, each of which optionallycontains an oxygen atom. By using a bromine compound or an iodinecompound, iodine or bromine is introduced into the polymer, and servesas a crosslinking point.

Examples of the bromine compound or the iodine compound include1,3-diiodoperfluoropropane, 2-iodoperfluoropropane,1,3-diiodo-2-chloroperfluoropropane, 1,4-diiodoperfluorobutane,1,5-diiodo-2,4-dichloroperfluoropentane, 1,6-diiodoperfluorohexane,1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane,1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoethane,1,3-diiodo-n-propane, CF₂Br₂, BrCF₂CF₂Br, CF₃CFBrCF₂Br, CFClBr₂,BrCF₂CFClBr, CFBrClCFClBr, BrCF₂CF₂CF₂Br, BrCF₂CFBrOCF₃,1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane,1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane,3-brcmo-4-iodoperfluorobutene-1,2-bromo-4-iodoperfluorobutene-1, and amonoiodo- and monobromo-substitution product, diiodo- andmonobromo-substitution product, and (2-iodoethyl)- and(2-bromoethyl)-substitution product of benzene. These compounds may beused alone or in any combination.

Among these, the chain transfer agent is preferably at least oneselected from the group consisting of alkanes and alcohols from theviewpoints of polymerization reactivity, crosslinkablility,availability, and the like. The alkane preferably has 1 to 6, morepreferably 1 to 5, still more preferably 2 to 4, and further preferably3 to 4 carbon atoms. The alcohol preferably has 1 to 5 carbon atoms,more preferably 1 to 4 carbon atoms, and still more preferably 3 to 4carbon atoms. The chain transfer agent is preferably at least oneselected from the group consisting of alcohols having 1 to 4 carbonatoms and alkanes having 2 to 4 carbon atoms, and is particularlypreferably at least one selected from the group consisting of methane,ethane, propane, isobutane, methanol, ethanol, and isopropanol.

The amount of the chain transfer agent is preferably 0.001 to 10,000mass ppm based on the aqueous medium. The amount of the chain transferagent is more preferably 0.01 mass ppm or more, still more preferably0.05 mass ppm or more, further preferably 0.1 mass ppm or more, andparticularly preferably 0.5 mass ppm or more based on the aqueousmedium. The amount of the chain transfer agent is more preferably 1,000mass ppm or less, still more preferably 500 mass ppm or less, furtherpreferably 100 mass ppm or less, and particularly preferably 10 mass ppmor less based on the aqueous medium.

The chain transfer agent may be added to the reaction vessel at oncebefore initiation of the polymerization, may be added at once afterinitiation of the polymerization, may be added in multiple portionsduring the polymerization, or may be added continuously during thepolymerization.

When a chain transfer agent and a nonionic surfactant are used as thenucleating agent, the mass ratio of the chain transfer agent to thenonionic surfactant (chain transfer agent/nonionic surfactant) ispreferably 1,000/1 to 1/5, more preferably 200/1 to 1/2, 100/1 to 1/1,and still more preferably 50/1 to 2/1 because more particles can begenerated during polymerization, and primary particles having a smalleraverage primary particle size and aspect ratio can be obtained.

Also, in the production method of the present disclosure, in addition tothe polymer (I) and other compounds having a surfactant function used asnecessary, an additive may also be used to stabilize the compounds.Examples of the additive include a buffer, a pH adjuster, a stabilizingaid, and a dispersion stabilizer.

The stabilizing aid is preferably paraffin wax, fluorine-containing oil,a fluorine-containing solvent, silicone oil, or the like. Thestabilizing aids may be used alone or in combination of two or more. Thestabilizing aid is more preferably paraffin wax. The paraffin wax may bein the form of liquid, semi-solid, or solid at room temperature, and ispreferably a saturated hydrocarbon having 12 or more carbon atoms. Theparaffin wax usually preferably has a melting point of 40 to 65° C., andmore preferably 50 to 65° C.

The amount of the stabilizing aid used is preferably 0.1 to 12% by mass,and more preferably 0.1 to 8% by mass, based on the mass of the aqueousmedium used. It is desirable that the stabilizing aid is sufficientlyhydrophobic so that the stabilizing aid is completely separated from thedispersion of modified PTFE after polymerization of modified PTFE, anddoes not serve as a contaminating component. Further, the stabilizingaid is preferably removed from the aqueous dispersion obtained bypolymerization.

Examples of the pH adjuster include ammonia, sodium hydroxide, potassiumhydroxide, sodium carbonate, potassium carbonate, anonium carbonate,sodium hydrogen carbonate, potassium hydrogen carbonate, ammoniumhydrogen carbonate, sodium phosphate, potassium phosphate, sodiumcitrate, potassium citrate, ammonium citrate, sodium gluconate,potassium gluconate, and ammonium gluconate. The pH can be measured by apH meter manufactured by Orion.

The pH of the aqueous medium when polymerizing TFE is preferably basic.The pH of the aqueous medium may be adjusted by adding a pH adjuster tothe aqueous medium. The pH of the aqueous medium when polymerizing TFEis preferably 7.1 or higher, and more preferably 7.5 or higher. Byadjusting the pH to be basic, the stability increasing effect on theaqueous dispersion due to the presence of the polymer (I) is furtherenhanced, and the polymerization of TFE in the aqueous medium proceedsmore smoothly.

In the polymerization of TFE, TFE may be polymerized in the presence ofan anionic hydrocarbon surfactant. By using an anionic hydrocarbonsurfactant, the stability of the aqueous dispersion produced by thepolymerization is enhanced, and the polymerization of TFE proceedssmoothly.

In the polymerization of TFE, TFE may be polymerized substantially inthe absence of an anionic hydrocarbon surfactant. In the polymerizationof TFE performed in the presence of the polymer (I), the polymerizationof TFE proceeds smoothly without using an anionic hydrocarbonsurfactant.

The expression “substantially in the absence of an anionic hydrocarbonsurfactant” as used herein means that the amount of the anionichydrocarbon surfactant in the aqueous medium is 10 mass ppm or less,preferably 1 mass ppm or less, more preferably 100 mass ppb or less,still more preferably 10 mass ppb or less, and further preferably 1 massppb or less.

Anionic hydrocarbon surfactants usually have a hydrophilic moiety suchas a carboxylate, a sulfonate or a sulfate and a hydrophobic moiety thatis a long chain hydrocarbon moiety such as alkyl.

Examples of the anionic hydrocarbon surfactant include Versatic® 10manufactured by Resolution Performance Products, and Avanel S series(S-70, S-74, etc.) manufactured by BASF.

Examples of the anionic hydrocarbon surfactant include an anionicsurfactant represented by R-L-M, wherein R is a linear or branched alkylgroup having one or more carbon atoms and optionally having asubstituent, or a cyclic alkyl group having 3 or more carbon atoms andoptionally having a substituent, and optionally contains a monovalent ordivalent heterocycle or optionally forms a ring when having 3 or morecarbon atoms; L is —ArSO₃—, —SO₃—, —SO₄—, —PO₃ or COO—, and, M is, H, ametal atom, NR⁵ ₄, imidazolium optionally having a substituent,pyridinium optionally having a substituent, or phosphonium optionallyhaving a substituent, wherein R⁵ is H or an organic group, and —ArSO₃ isan aryl sulfonate.

Specific examples thereof include a compound represented byCH₃—(CH₂)_(n)-L-M, wherein n is an integer of 6 to 17, as represented bylauryl acid and lauryl sulfate. L and M are the same as described above.Mixtures of those in which R is an alkyl group having 12 to 16 carbonatoms and L-M is sulfate or sodium dodecyl sulfate (SDS) can also beused.

Further, examples of the anionic hydrocarbon surfactant include ananionic surfactant represented by R⁶(-L-M)₂, wherein R⁶ is a linear orbranched alkyl group having one or more carbon atoms and optionallyhaving a substituent, or a cyclic alkylene group having 3 or more carbonatoms and optionally having a substituent, and optionally contains amonovalent or divalent heterocycle or optionally forms a ring whenhaving 3 or more carbon atoms; L is —ArSO₃—, —SO₃—, —SO₄—, —PO₃ or COO—,and, M is, H, a metal atom, NR⁵ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent, wherein R⁵ is H or an organic group,and —ArSO₃ is an aryl sulfonate.

Further, examples of the anionic hydrocarbon surfactant include ananionic surfactant represented by R⁷(-L-M)₃, wherein R⁷ is a linear orbranched alkylidine group having one or more carbon atoms and optionallyhaving a substituent, or a cyclic alkylidine group having 3 or morecarbon atoms and optionally having a substituent, and optionallycontains a monovalent or divalent heterocycle or optionally forms a ringwhen having 3 or more carbon atoms; L is —ArSO₃—, —SO₃—, —SO₄—, —PO₃— orCOO—, and, M is, H, a metal atom, NR⁵ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent, R⁵ is H or an organic group; and—ArSO₃— is an aryl sulfonate.

Further, examples of the anionic hydrocarbon surfactant include asiloxane hydrocarbon surfactant. Examples of the siloxane hydrocarbonsurfactant include those described in Silicone Surfactants, R. S. M.Hill, Marcel Dekker, Inc., ISBN: 0-8247-00104. The structure of thesiloxane hydrocarbon surfactant includes defined hydrophobic andhydrophilic moieties. The hydrophobic moiety contains one or moredihydrocarbyl siloxane units, where the substituents on the siliconeatoms are completely hydrocarbon. In the sense that the carbon atoms ofthe hydrocarbyl groups are fully substituted with hydrogen atoms wherethey can be substituted by halogen such as fluorine, these siloxanesurfactants can also be regarded as hydrocarbon surfactants, i.e. themonovalent substituents on the carbon atoms of the hydrocarbyl groupsare hydrogen.

The hydrophilic moiety of the siloxane hydrocarbon surfactant maycontain one or more polar moieties including ionic groups such assulfate, sulfonate, phosphonate, phosphate ester, carboxylate,carbonate, sulfosuccinate, taurate (as the free acid, a salt or anester), phosphine oxides, betaine, betaine copolyol, or quaternaryammonium salts. Ionic hydrophobic moieties may also contain ionicallyfunctionalized siloxane grafts. Examples of such siloxane hydrocarbonsurfactants include polydimethylsiloxane-graft-(meth)acrylic acid salts,polydimethylsiloxane-graft-polyacrylate salts, andpolydimethylsiloxane-grafted quaternary amines. The polar moieties ofthe hydrophilic moiety of the siloxane hydrocarbon surfactant maycontain nonionic groups formed by polyethers, such as polyethylene oxide(PEO), and mixed polyethylene oxide/polypropylene oxide polyethers(PEO/PPO); mono- and disaccharides; and water-soluble heterocycles suchas pyrrolidinone. The ratio of ethylene oxide to propylene oxide (EO/PO)may be varied in mixed polyethylene oxide/polypropylene oxidepolyethers.

The hydrophilic moiety of the siloxane hydrocarbon surfactant may alsocontain a combination of ionic and nonionic moieties. Such moietiesinclude, for example, ionically end-functionalized or randomlyfunctionalized polyether or polyol. Preferable is a siloxane having anonionic moiety, i.e., a nonionic siloxane surfactant.

The arrangement of the hydrophobic and hydrophilic moieties of thestructure of a siloxane hydrocarbon surfactant may take the form of adiblock polymer (AB), triblock polymer (ABA), wherein the “B” representsthe siloxane portion of the molecule, or a multi-block polymer.Alternatively, the siloxane surfactant may include a graft polymer.

The siloxane hydrocarbon surfactants also include those disclosed inU.S. Pat. No. 6,841,616.

Examples of the siloxane-based anionic hydrocarbon surfactant includeNoveon® by Lubrizol Advanced Materials, Inc. and SilSensem PE-100silicone and SilSense™ CA-1 silicone available from ConsumerSpecialties.

Examples of the anionic hydrocarbon surfactant also include asulfosuccinate surfactant Lankropol® K8300 by Akzo Nobel SurfaceChemistry LLC. Examples of the sulfosuccinate surfactant include sodiumdiisodecyl sulfosuccinate (Emulsogen® SB10 by Clariant) and sodiumdiisotridecyl sulfosuccinate (Polirol® TR/LNA by Cesapinia Chemicals).

Examples of the anionic hydrocarbon surfactants also include PolyFox®surfactants by Omnova Solutions, Inc. (PolyFox™ PF-156A, PolyFox™PF-136A, etc.).

The anionic hydrocarbon surfactant includes a compound (α) representedby the following formula (α):

R¹⁰—COOM  (α)

wherein R¹⁰ is a monovalent organic group containing one or more carbonatoms; and M is H, a metal atom, NR¹¹ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent, wherein R¹¹ is H or an organic groupand may be the same or different. R¹¹ is preferably H or a C₁₋₁₀ organicgroup, and more preferably H or a C₁₋₄ organic group.

From the viewpoint of surfactant function, the number of carbon atoms inR¹⁰ is preferably 2 or more, and more preferably 3 or more. From theviewpoint of water-solubility, the number of carbon atoms in R¹⁰ ispreferably 29 or less, and more preferably 23 or less. Examples of themetal atom as M include alkali metals (Group 1) and alkaline earthmetals (Group 2), and preferred is Na, K, or Li. M is preferably H, ametal atom, or NR¹¹ ₄, more preferably H, an alkali metal (Group 1), analkaline earth metal (Group 2), or NR¹¹ ₄, still more preferably H, Na,K, Li, or NH₄, further preferably Na, K, or NH₄, particularly preferablyNa or NH₄, and most preferably NH₄.

Examples of the compound (α) include R¹²—COOM, wherein R¹² is a linearor branched, alkyl group, alkenyl group, alkylene group, or alkenylenegroup having 1 or more carbon atoms and optionally having a substituent,or a cyclic alkyl group, alkenyl group, alkylene group, or alkenylenegroup having 3 or more carbon atoms and optionally having a substituent,each of which optionally contains an ether bond; when having 3 or morecarbon atoms, R¹² optionally contains a monovalent or divalentheterocycle, or optionally forms a ring; and M is as described above.Specific examples thereof include a compound represented byCH₃—(CH₂)_(n)—COOM, wherein n is an integer of 2 to 28, and M is asdescribed above.

From the viewpoint of emulsion stability, the compound (α) is preferablyfree from a carbonyl group which is not in a carboxyl group. Preferableexamples of the hydrocarbon-containing surfactant free from a carbonylgroup include a compound of the following formula (A):

R—COO-M  (A)

wherein R is an alkyl group, an alkenyl group, an alkylene group, or analkenylene group containing 6 to 17 carbon atoms, each of whichoptionally contains an ether bond; M is H, a metal atom, NR¹¹ ₄,imidazolium optionally having a substituent, pyridinium optionallyhaving a substituent, or phosphonium optionally having a substituent;and R¹¹ is the same or different and is H or an organic group having 1to 10 carbon atoms. In the formula (A), R is preferably an alkyl groupor an alkenyl group, each of which optionally contains an ether group.The alkyl group or alkenyl group for R may be linear or branched. Thenumber of carbon atoms in R may be, but is not limited to, 2 to 29.

When the alkyl group is linear, the number of carbon atoms in R ispreferably 3 to 29, and more preferably 5 to 23. When the alkyl group isbranched, the number of carbon atoms in R is preferably 5 to 35, andmore preferably 11 to 23. When the alkenyl group is linear, the numberof carbon atoms in R is preferably 2 to 29, and more preferably 9 to 23.When the alkenyl group is branched, the number of carbon atoms in R ispreferably 2 to 29, and more preferably 9 to 23.

Examples of the alkyl group and the alkenyl group include a methylgroup, an ethyl group, an isobutyl group, a t-butyl group, and a vinylgroup.

Further, the anionic hydrocarbon surfactant may also be a carboxylicacid-type hydrocarbon surfactant. Examples of the carboxylic acid-typehydrocarbon surfactant include butylic acid, valeric acid, caproic acid,enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid,myristic acid, pentadecylic acid, palmitic acid, palmitoleic acid,margaric acid, stearic acid, oleic acid, vaccenic acid, linoleic acid,(9,12,15)-linolenic acid, (6,9,12) linolenic acid, eleostearic acid,arachidic acid, 8,11-eicosadienoic acid, mead acid, arachidonic acid,behenic acid, lignoceric acid, nervonic acid, cerotic acid, montanicacid, melissic acid, crotonic acid, myristoleic acid, palmitoleic acid,sapienoic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid,eicosenoic acid, erucic acid, nervonic acid, linoleic acid,eicosadienoic acid, docosadienoic acid, linolenic acid, pinolenic acid,α-eleostearic acid, β-eleostearic acid, mead acid, dihomo-γ-linolenicacid, eicosatrienoic acid, stearidonic acid, arachidonic acid,eicosatetraenoic acid, adrenic acid, boseopentaenoic acid,eicosapentaenoic acid, osbond acid, sardine acid, tetracosapentaenoicacid, docosahexaenoic acid, nisinic acid, and salts thereof.Particularly, preferred is at least one selected from the groupconsisting of lauric acid, capric acid, myristic acid, pentadecylicacid, palmitic acid, and salts thereof. Examples of the salts include,but are not limited to, those in which hydrogen of the carboxyl group isa metal atom, NR¹¹ ₄, imidazolium optionally having a substituent,pyridinium optionally having a substituent, or phosphonium optionallyhaving a substituent as M in the formula described above.

Further, the anionic hydrocarbon surfactants may be, for example,anionic hydrocarbon surfactants disclosed in International PublicationNo. WO2013/146950 and International Publication No. WO2013/146947.Examples thereof include those having a saturated or unsaturatedaliphatic chain having 6 to 40 carbon atoms, preferably 8 to 20 carbonatoms, and more preferably 9 to 13 carbon atoms. The saturated orunsaturated aliphatic chain may be either linear or branched, or mayhave a cyclic structure. The hydrocarbon may have aromaticity, or mayhave an aromatic group. The hydrocarbon may contain a hetero atom suchas oxygen, nitrogen, or sulfur.

Examples of the anionic hydrocarbon surfactants include alkylsulfonates, alkyl sulfates, and alkyl aryl sulfates, and salts thereof;aliphatic (carboxylic) acids and salts thereof; and phosphoric acidalkyl esters and phosphoric acid alkyl aryl esters, and salts thereof.Of these, preferred are alkyl sulfonates, alkyl sulfates, and aliphaticcarboxylic acids, and salts thereof.

Preferable examples of the alkyl sulfates and salts thereof includeammonium lauryl sulfate and sodium lauryl sulfate.

Preferable examples of the aliphatic carboxylic acids or salts thereofinclude succinic acid, decanoic acid, undecanoic acid, undecenoic acid,lauric acid, hydrododecanoic acid, or salts thereof.

The polymerization in the production method may be performed by charginga polymerization reactor with an aqueous medium, the polymer (I),tetrafluoroethylene, a modifying monomer, and optionally otheradditives, stirring the contents of the reactor, maintaining the reactorat a predetermined polymerization temperature, and adding apredetermined amount of a polymerization initiator to thereby initiatethe polymerization reaction. After the initiation of the polymerizationreaction, the components such as the monomers, the polymerizationinitiator, a chain transfer agent, and the surfactant may additionallybe added depending on the purpose. The polymer (I) may be added afterthe polymerization reaction is initiated.

The polymerization initiator may be any polymerization initiator capableof generating radicals within the polymerization temperature range, andknown oil-soluble and/or water-soluble polymerization initiators may beused. The polymerization initiator may be combined with a reducingagent, for example, to form a redox agent, which initiates thepolymerization. The concentration of the polymerization initiator isappropriately determined depending on the types of the monomers, themolecular weight of the target modified PTFE, and the reaction rate.

The polymerization initiator to be used may be an oil-soluble radicalpolymerization initiator or a water-soluble radical polymerizationinitiator.

The oil-soluble radical polymerization initiator may be a knownoil-soluble peroxide, and representative examples thereof includedialkyl peroxycarbonates such as diisopropyl peroxydicarbonate anddi-sec-butyl peroxydicarbonate; peroxy esters such as t-butylperoxyisobutyrate and t-butyl peroxypivalate; and dialkyl peroxides suchas di-t-butyl peroxide, as well as di[perfluoro (or fluorochloro) acyl]peroxides such as di(ω-hydro-dodecafluoroheptanoyl)peroxide,di(ω-hydro-tetradecafluoroheptanoyl)peroxide,di(ω-hydro-hexadecafluorononanoyl)peroxide,di(perfluorobutyryl)peroxide, di(perfluorovaleryl)peroxide,di(perfluorohexanoyl)peroxide, di(perfluoroheptanoyl)peroxide,di(perfluorooctanoyl)peroxide, di(perfluorononanoyl)peroxide,di(ω-chloro-hexafluorobutyryl)peroxide,di(ω-chloro-decafluorohexanoyl)peroxide,di(ω-chloro-tetradecafluorooctanoyl)peroxide,ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide,ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide,ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide,di(dichloropentafluorobutanoyl)peroxide,di(trichlorooctafluorohexanoyl)peroxide,di(tetrachloroundecafluorcoctanoyl)peroxide,di(pentachlorotetradecafluorodecanoyl)peroxide, anddi(undecachlorodotoriacontafluorodocosanoyl)peroxide.

The water-soluble radical polymerization initiator may be a knownwater-soluble peroxide, and examples thereof include ammonium salts,potassium salts, and sodium salts of persulphuric acid, perboric acid,perchloric acid, perphosphoric acid, and percarbonic acid, organicperoxides of disuccinic acid peroxide and diglutaric acid peroxide,t-butyl permaleate, and t-butyl hydroperoxide. A reducing agent such asa sulfite or a sulfurous acid salt may be contained together, and theamount thereof may be 0.1 to 20 times the amount of the peroxide.

For example, in a case where the polymerization is performed at a lowtemperature of 30° C. or lower, the polymerization initiator used ispreferably a redox initiator obtained by combining an oxidizing agentand a reducing agent. Examples of the oxidizing agent includepersulfates, organic peroxides, potassium permanganate, manganesetriacetate, anonium cerium nitrate, and bromate. Examples of thereducing agent include sulfites, bisulfites, bromates, diimine, andoxalic acid. Examples of the persulfates include anonium persulfate andpotassium persulfate. Examples of the sulfite include sodium sulfite andammonium sulfite. In order to increase the decomposition rate of theinitiator, the combination of the redox initiator may preferably containa copper salt or an iron salt. An example of the copper salt iscopper(II) sulfate and an example of the iron salt is iron(II) sulfate.

Examples of the redox initiator include potassium permanganate/oxalicacid, ammonium persulfate/bisulfite/iron(II) sulfate, ammoniumpersulfate/sulfite/iron(II) sulfate, ammonium persulfate/sulfite,ammonium persulfate/iron(II) sulfate, manganese triacetate/oxalic acid,ammonium cerium nitrate/oxalic acid, bromate/sulfite, andbromate/bisulfite, and potassium permanganate/oxalic acid and ammoniumpersulfate/sulfite/iron(II) sulfate are preferable. In the case of usinga redox initiator, either an oxidizing agent or a reducing agent may becharged into a polymerization tank in advance, followed by adding theother continuously or intermittently thereto to initiate thepolymerization. For example, in the case of potassiumpermanganate/oxalic acid, preferably, oxalic acid is charged into apolymerization tank and potassium permanganate is continuously addedthereto.

The polymerization initiator may be added in any amount, and theinitiator in an amount that does not significantly decrease thepolymerization rate (e.g., several parts per million in water) or moremay be added at once in the initial stage of polymerization, or may beadded successively or continuously. The upper limit thereof falls withina range where the reaction temperature is allowed to increase while thepolymerization reaction heat is removed through the device surfaces. Theupper limit thereof is more preferably within a range where thepolymerization reaction heat can be removed through the device surfaces.

The aqueous medium is a reaction medium in which the polymerization isperformed, and means a liquid containing water. The aqueous medium maybe any medium containing water, and it may be one containing water and,for example, any of fluorine-free organic solvents such as alcohols,ethers, and ketones, and/or fluorine-containing organic solvents havinga boiling point of 40° C. or lower.

In the polymerization step, tetrafluoroethylene and a modifying monomerare preferably polymerized substantially in the absence of afluorine-containing surfactant. Conventionally, fluorine-containingsurfactants have been used in the polymerization for modifiedpolytetrafluoroethylene, but the production method of the presentdisclosure allows for obtaining modified polytetrafluoroethylene byusing the polymer (I) even without using the fluorine-containingsurfactants. The expression “substantially in the absence of afluorine-containing surfactant” as used herein means that the amount ofthe fluorine-containing surfactant in the aqueous medium is 10 mass ppmor less, preferably 1 mass ppm or less, more preferably 100 mass ppb orless, still more preferably 10 mass ppb or less, and further preferably1 mass ppb or less.

Examples of the fluorine-containing surfactant include anionicfluorine-containing surfactants.

The anionic fluorine-containing surfactant may be, for example, afluorine atom-containing surfactant having 20 or less carbon atoms intotal in the portion excluding the anionic group.

The fluorine-containing surfactant may also be a fluorine-containingsurfactant having an anionic moiety having a molecular weight of 800 orless.

The “anionic moiety” means the portion of the fluorine-containingsurfactant excluding the cation. For example, in the case ofF(CF₂)_(n1)COOM represented by the formula (I) described later, theanionic moiety is the “F(CF₂)_(n1)COO” portion.

Examples of the fluorine-containing surfactant also includefluorine-containing surfactants having a Log POW of 3.5 or less. The LogPOW is a partition coefficient between 1-octanol and water, which isrepresented by Log P (wherein P is the ratio between the concentrationof the fluorine-containing surfactant in octanol and the concentrationof the fluorine-containing surfactant in water in a phase-separatedoctanol/water (1:1) liquid mixture containing the fluorine-containingsurfactant). Log POW is determined as follows. Specifically, HPLC isperformed on standard substances (heptanoic acid, octanoic acid,nonanoic acid, and decanoic acid) each having a known octanol/waterpartition coefficient using TOSOH ODS-120T (4.6 mm×250 mm, Tosoh Corp.)as a column and acetonitrile/0.6% by mass HClO₄ aqueous solution (=1/1(vol/vol %)) as an eluent at a flow rate of 1.0 ml/min, a sample amountof 300 μL, and a column temperature of 40° C.; with a detection light ofUV 210 nm. For each standard substance, a calibration curve is drawnwith respect to the elution time and the known octanol/water partitioncoefficient. Based on the calibration curve, Log POW is calculated fromthe elution time of the sample liquid in HPLC.

Specific examples of the fluorine-containing surfactant include thosedisclosed in U.S. Patent Application Publication No. 2007/0015864, U.S.Patent Application Publication No. 2007/0015865, U.S. Patent ApplicationPublication No. 2007/0015866, and U.S. Patent Application PublicationNo. 2007/0276103, U.S. Patent Application Publication No. 2007/0117914,U.S. Patent Application Publication No. 2007/142541, U.S. PatentApplication Publication No. 2008/0015319, U.S. Pat. Nos. 3,250,808,3,271,341, Japanese Patent Laid-Open No. 2003-119204, InternationalPublication No. WO2005/042593, International Publication No.WO2008/060461, International Publication No. WO2007/046377,International Publication No. WO2007/119526, International PublicationNo. WO2007/046482, International Publication No. WO2007/046345, U.S.Patent Application Publication No. 2014/0228531, InternationalPublication No. WO2013/189824, and International Publication No.WO2013/189826.

Examples of the anionic fluorine-containing surfactant include acompound represented by the following general formula (N⁰):

X^(n0)—Rf^(n0)—Y⁰  (N⁰)

wherein X^(n0) is H, Cl, or F; Rf^(n0) is a linear, branched, or cyclicalkylene group having 3 to 20 carbon atoms in which some or all of Hsare replaced by F; the alkylene group optionally containing one or moreether bonds in which some of Hs are replaced by Cl; and Y⁰ is an anionicgroup.

The anionic group Y⁰ may be —COOM, —SO₂M, or —SO₃M, and may be —COOM or—SO₃M.

M is H, a metal atom, NR⁷ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent, and R⁷ is H or an organic group.Examples of the metal atom include alkali metals (Group 1) and alkalineearth metals (Group 2), such as Na, K, or Li.

R⁷ may be H or a C₁₋₁₀ organic group, may be H or a C₁₋₄ organic group,and may be H or a C₁₋₄ alkyl group.

M may be H, a metal atom, or NR⁷ ₄, may be H, an alkali metal (Group 1),an alkaline earth metal (Group 2), or NR⁷ ₄, and may be H, Na, K, Li, orNH₄.

Rf^(n0) may be one in which 50% or more of H has been replaced byfluorine.

Examples of the compound represented by the general formula (N⁰)include:

a compound represented by the following general formula (N¹):

X^(n0)—(CF₂)_(m1)—Y⁰  (N¹)

wherein X⁰ is H, Cl, and F; m1 is an integer of 3 to 15; and Y⁰ is asdefined above;

a compound represented by the following general formula (N²):

Rf^(n1)—O—(CF(CF₃)CF₂O)_(m2)CFX^(n1)—Y⁰  (N²)

wherein Rf^(n1) is a perfluoroalkyl group having 1 to 5 carbon atoms; m2is an integer of 0 to 3; X^(n1) is F or CF₃; and Y⁰ is as defined above;a compound represented by the following general formula (N³):

Rf^(n2)(CH₂)_(m3)—(Rf^(n3))_(q)—Y⁰  (N³)

wherein Rf^(n2) is a partially or fully fluorinated alkyl group having 1to 13 carbon atoms and optionally containing an ether bond; m3 is aninteger of 1 to 3; Rf^(n3) is a linear or branched perfluoroalkylenegroup having 1 to 3 carbon atoms; q is 0 or 1; and Y⁰ is as definedabove; a compound represented by the following general formula (N⁴):

Rf^(n4)—O—(CY^(n1)Y^(n2))_(p)CF₂—Y⁰  (N⁴)

wherein Rf^(n4) is a linear or branched partially or fully fluorinatedalkyl group having 1 to 12 carbon atoms and optionally containing anether bond; and Y_(n1) and Y, are the same or different and are each Hor F; p is 0 or 1; and Y⁰ is as defined above; and

a compound represented by the following general formula (N⁵):

wherein X^(n2), X¹³, and X⁴ may be the same or different and are each H,F, or a linear or branched partial or fully fluorinated alkyl grouphaving 1 to 6 carbon atoms and optionally containing an ether bond;Rf^(n5) is a linear or branched partially or fully fluorinated alkylenegroup having 1 to 3 carbon atoms and optionally containing an etherbond; L is a linking group; and Y⁰ is as defined above, with the provisothat the total carbon number of X^(n2), X^(n3), X^(n4), and Rf^(h5) is18 or less.

More specific examples of the compound represented by general formula(N⁰) include a perfluorocarboxylic acid (I) represented by the followinggeneral formula (I), an ω-H perfluorocarboxylic acid (II) represented bythe following general formula (II), a perfluoropolyethercarboxylic acid(III) represented by the following general formula (III), aperfluoroalkylalkylenecarboxylic acid (IV) represented by the followinggeneral formula (IV), a perfluoroalkoxyfluorocarboxylic acid (V)represented by the following general formula (V), aperfluoroalkylsulfonic acid (VI) represented by the following generalformula (VI), an ω-H perfluorosulfonic acid (VII) represented by thefollowing general formula (VII), a perfluoroalkylalkylene sulfonic acid(VIII) represented by the following general formula (VIII), analkylalkylene carboxylic acid (IX) represented by the following generalformula (IX), a fluorocarboxylic acid (X) represented by the followinggeneral formula (X), an alkoxyfluorosulfonic acid (XI) represented bythe following general formula (XI), a compound (XII) represented by thegeneral formula (XII), and a compound (XIII) represented by the generalformula (XIII).

The perfluorocarboxylic acid (I) is represented by the following generalformula (I):

F(CF₂)_(n1)COOM  (I)

wherein n1 is an integer of 3 to 14; and M is H, a metal atom, NR⁷ ₄,imidazolium optionally having a substituent, pyridinium optionallyhaving a substituent, or phosphonium optionally having a substituent,and R⁷ is H or an organic group.

The ω-H perfluorocarboxylic acid (II) is represented by the followinggeneral formula (II):

H(CF₂)_(n2)COOM  (II)

wherein n2 is an integer of 4 to 15; and M is as defined above.

The perfluoropolyethercarboxylic acid (III) is represented by thefollowing general formula (III):

Rf¹—O—(CF(CF₃)CF₂O)_(n3)CF(CF₃)COOM  (III)

wherein Rf¹ is a perfluoroalkyl group having 1 to 5 carbon atoms; n3 isan integer of 0 to 3; and M is as defined above.

The perfluoroalkylalkylenecarboxylic acid (IV) is represented by thefollowing general formula (IV):

Rf²(CH₂)_(n4)Rf³COOM  (IV)

wherein Rf² is a perfluoroalkyl group having 1 to 5 carbon atoms; Rf³ isa linear or branched perfluoroalkylene group having 1 to 3 carbon atoms;n4 is an integer of 1 to 3; and M is as defined above.

The alkoxyfluorocarboxylic acid (V) is represented by the followinggeneral formula (V):

Rf⁴—O—CY¹Y²CF₂—COOM  (V)

wherein Rf⁴ is a linear or branched partially or fully fluorinated alkylgroup having 1 to 12 carbon atoms and optionally containing an etherbond; Y¹ and Y² are the same or different and are each H or F; and M isas defined above.

The perfluoroalkylsulfonic acid (VI) is represented by the followinggeneral formula (VI):

F(CF₂)_(n5)SO₃M  (VI)

wherein n5 is an integer of 3 to 14; and M is as defined above.

The ω-H perfluorosulfonic acid (VII) is represented by the followinggeneral formula (VII):

H(CF₂)_(n6)SO₃M  (VII)

wherein n6 is an integer of 4 to 14; and M is as defined above.

The perfluoroalkylalkylenesulfonic acid (VIII) is represented by thefollowing general formula (VIII):

Rf⁵(CH₂)_(n7)SO₃M  (VIII)

wherein Rf⁵ is a perfluoroalkyl group having 1 to 13 carbon atoms; n7 isan integer of 1 to 3; and M is as defined above.

The alkylalkylenecarboxylic acid (IX) is represented by the followinggeneral formula (IX):

Rf⁶(CH₂)_(n8)COOM  (IX)

wherein Rf⁶ is a linear or branched partially or fully fluorinated alkylgroup having 1 to 13 carbon atoms and optionally containing an etherbond; n8 is an integer of 1 to 3; and M is as defined above.

The fluorocarboxylic acid (X) is represented by the following generalformula (X):

Rf⁷—O—Rf⁸—O—CF₂—COOM  (X)

wherein Rf⁷ is a linear or branched partially or fully fluorinated alkylgroup having 1 to 6 carbon atoms and optionally containing an etherbond; Rf⁸ is a linear or branched partially or fully fluorinated alkylgroup having 1 to 6 carbon atoms; and M is as defined above.

The alkoxyfluorosulfonic acid (XI) is represented by the followinggeneral formula (XI):

Rf⁹—O—CY¹Y²CF₂—SO₃M  (XI)

wherein Rf⁹ is a linear or branched partially or fully fluorinated alkylgroup having 1 to 12 carbon atoms and optionally containing an etherbond and optionally containing chlorine; Y¹ and Y² are the same ordifferent and are each H or F; and M is as defined above.

The compound (XII) is represented by the following general formula(XII):

wherein X¹, X², and X³ may be the same or different and are H, F, and alinear or branched partially or fully fluorinated alkyl group having 1to 6 carbon atoms and optionally containing an ether bond; Rf¹⁰ is aperfluoroalkylene group having 1 to 3 carbon atoms; L is a linkinggroup; and Y⁰ is an anionic group.

Y⁰ may be —COOM, —SO₂M, or —SO₃M, and may be —SO₃M or COOM, where M isas defined above.

Examples of L include a single bond, a partially or fully fluorinatedalkylene group having 1 to 10 carbon atoms and optionally containing anether bond.

The compound (XIII) is represented by the following general formula(XIII):

Rf¹¹—O—(CF₂CF(CF₃)O)_(n9)(CF₂O)_(n10)CF₂COOM  (XIII)

wherein Rf¹¹ is a fluoroalkyl group having 1 to 5 carbon atomscontaining chlorine, n9 is an integer of 0 to 3, n10 is an integer of 0to 3, and M is the same as defined above. Examples of the compound(XIII) include CF₂ClO(CF₂CF(CF₃)O)_(n9)(CF₂O)_(n10)CF₂COONH₄ (mixturehaving an average molecular weight of 750, in the formula, n9 and n10are defined above).

As described above, examples of the anionic fluorine-containingsurfactant include a carboxylic acid-based surfactant and a sulfonicacid-based surfactant.

In the production method of the present disclosure, in particular, it ispreferable that the modifying monomer includes at least one selectedfrom the group consisting of hexafluoropropylene, perfluoro(alkyl vinylether) and (perfluoroalkyl)ethylene, and the polymerization temperatureis 10 to 150° C.; and the production method preferably further includesthe step of adding the modifying monomer to a reactor before theinitiation of polymerization or when the concentration of particles ofmodified polytetrafluoroethylene formed in the aqueous medium is 5.0% bymass or less, preferably 3.0% by mass or less, more preferably 1.0% bymass or less, still more preferably 0.5% by mass or less, andparticularly preferably at the same time as the initiation of thepolymerization.

In the production method of the present disclosure, it is alsopreferable that the modifying monomer includes the modifying monomer(A), and the polymerization temperature is 10 to 150° C.; and theproduction method preferably further includes the step of adding themodifying monomer to the reactor before the initiation of polymerizationor when the concentration of particles of modifiedpolytetrafluoroethylene formed in the aqueous medium is 5.0% by mass orless, preferably 3.0% by mass or less, more preferably 1.0% by mass orless, still more preferably 0.5% by mass or less, and particularlypreferably at the same time as the initiation of the polymerization.

In the polymerization step, it is preferable to generate 0.6×10¹³particles/ml or more of particles. By generating a large number ofparticles in the polymerization step, primary particles having a smallaverage primary particle size and a small aspect ratio can be obtained,and an aqueous dispersion having excellent stability can be obtained.The number of particles to be generated is 0.7×10¹³/mL or more,0.8×10¹³/mL or more, 0.9×10¹³/mL or more, 1.0×10¹³ particles/mL or more,and 1.5×10¹³ particles/mL or more in the order of preference. The upperlimit of the number of particles to be generated is not limited, but is,for example, 7.0×10¹⁴ particles/mL.

Since the particles generated by the polymerization of TFE areconcentrated in the first half of the polymerization and are unlikely tobe generated in the second half of the polymerization, the number ofparticles in the polymerization step is almost the same as the number ofparticles generated in the first half of the polymerization. Therefore,the number of particles in the polymerization step can be predicted bymeasuring the number of primary particles in the finally obtainedaqueous dispersion.

An aqueous dispersion of modified PTFE can be obtained by the method forproducing modified PTFE of the present disclosure. The solidconcentration of the aqueous dispersion of modified PTFE is not limited,but may be, for example, 1.0 to 70% by mass. The solid concentration ispreferably 8.0% by mass or more, more preferably 10.0% by mass or more,and more preferably 60.0% by mass or less, more preferably 50.0% by massor less. In the method for producing modified PTFE of the presentdisclosure, the adhesion amount to the finally obtained modified PTFE ispreferably 3.0% by mass or less, more preferably 2.0% by mass or less,more preferably 1.0% by mass or less, still more preferably 0.8% by massor less, further preferably 0.7% by mass or less, and particularlypreferably 0.6% by mass or less.

Next, applications and the like of PTFE obtained by the productionmethod of the present disclosure will now be described in more detail.

PTFE may be an aqueous dispersion of PTFE in which primary particles ofPTFE are dispersed in an aqueous medium.

Examples of the applications of the aqueous dispersion of modified PTFEinclude, but are not limited to, those in which the aqueous dispersionis directly used, such as coating achieved by applying the aqueousdispersion to a base material, drying the dispersion, and optionallysintering the workpiece; impregnation achieved by impregnating a poroussupport such as nonwoven fabric or a resin molded article with theaqueous dispersion, drying the dispersion, and preferably sintering theworkpiece; and casting achieved by applying the aqueous dispersion to abase material such as glass, drying the dispersion, optionally immersingthe workpiece into water to remove the base material and to therebyprovide a thin film. Examples of such applications include aqueousdispersion-type coating materials, tent membranes, conveyor belts,printed circuit boards (CCL), binders for electrodes, and waterrepellents for electrodes.

The aqueous dispersion of modified PTFE may be used in the form of anaqueous coating material for coating by mixing with a known compoundingagent such as a pigment, a thickener, a dispersant, a defoaming agent,an antifreezing agent, a film-forming aid, or by compounding anotherpolymer compound.

In addition, the aqueous dispersion may be used for additiveapplications, for example, for a binder application for preventing theactive material of an electrode from falling off, for a compoundapplication such as a drip inhibitor, or for a dust suppressingtreatment application for preventing floating of sand and dust.

The aqueous dispersion of modified PTFE is also preferably used as adust control treatment agent. The dust control treatment agent can beused in a method for suppressing dust of a dust-generating substance byfibrillating modified PTFE by mixing the mixture with thedust-generating substance and applying a compression-shearing action tothe mixture at a temperature of 20 to 200° C., for example, methodsdisclosed in Japanese Patent No. 2827152 and Japanese Patent No.2538783.

The aqueous dispersion of modified PTFE can be suitably used for, forexample, the dust control treatment agent composition described inInternational Publication No. WO2007/004250, and can be suitably usedfor the dust control treatment method described in InternationalPublication No. WO2007/000812.

The dust control treatment agent is suitably used in the fields ofbuilding-products, soil stabilizers, solidifying materials, fertilizers,landfill of incineration ash and harmful substance, explosion proofequipment, cosmetics, and sands for pet excretion represented by catsand.

The method for producing modified PTFE of the present disclosure mayinclude any of the step of concentrating an aqueous dispersion ofmodified PTFE obtained by the above-described method or subjecting theaqueous dispersion to dispersion stabilization treatment to obtain adispersion, and the step of dispersing a powder of modified PTFEobtained by the method described below in an aqueous medium in thepresence of a surfactant.

The method for producing modified PTFE of the present disclosuresuitably further includes at least one step among the step of recoveringthe aqueous dispersion of modified PTFE obtained by the method describedabove, the step of agglomerating modified PTFE in the aqueous dispersionof modified PTFE, the step of recovering the agglomerated modified PTFE,and the step of drying the recovered modified PTFE at 100 to 300° C. andpreferably 100 to 250° C. By including such a step, a powder of modifiedPTFE can be obtained.

The powder can be produced by agglomerating modified PTFE contained inthe aqueous dispersion. The aqueous dispersion of modified PTFE can beused as a powder for various purposes after being post-treated such asconcentration if necessary, and then agglomerated, washed, and dried.Agglomeration of the aqueous dispersion of the modified PTFE is usuallyperformed by diluting the aqueous dispersion obtained by polymerizationof polymer latex, for example, with water to a polymer concentration of10 to 20% by mass and preferably 10 to 20% by mass, optionally adjustingthe pH to a neutral or alkaline, and stirring the polymer morevigorously than during the reaction in a vessel equipped with a stirrer.The agglomeration may be performed under stirring while adding awater-soluble organic compound such as methanol or acetone, an inorganicsalt such as potassium nitrate or ammonium carbonate, or an inorganicacid such as hydrochloric acid, sulfuric acid, or nitric acid as acoagulating agent. The agglomeration may be continuously performed usinga device such as an inline mixer.

The aqueous dispersion of modified PTFE obtained by the productionmethod of the present disclosure has an average primary particle size offine modified PTFE particles of 100 to 500 nm, preferably 150 to 450 nm,and more preferably 200 to 400 nm.

When the average primary particle size of the fine modified PTFEparticles is small, the stability of the aqueous dispersion of modifiedPTFE is improved. However, when the aqueous dispersion of modified PTFEis excessively stabilized, time and labor are required to concentratethe aqueous dispersion of modified PTFE or to agglomerate the finemodified PTFE particles by applying stirring shearing force to theaqueous dispersion of modified PTFE to obtain a fine powder of modifiedPTFE, and thus the production efficiency is often impaired. Further,there is a problem in that when the average primary particle size offine modified PTFE particles is large, the stability of the aqueousdispersion of modified PTFE decreases and the amount of the agglomerateduring the polymerization of TFE increases, which is disadvantageous interms of productivity; when the aqueous dispersion of modified PTFE isconcentrated after the polymerization of TFE, a large amount of theagglomerate is generated in the concentration tank; the sedimentationstability of the concentration liquid is impaired and the storagestability is lowered; when the aqueous dispersion of modified PTFE isagitated by applying a stirring shearing force to the aqueous dispersionof modified PTFE to agglomerate the fine modified PTFE particles toobtain the fine powder of modified PTFE, a large amount of theagglomerate is generated before reaching the aggregation tank from thepolymerization tank and the piping is clogged; and the yield is greatlyreduced. When the average primary particle size of the fine modifiedPTFE particles is within the above range, the stability of the aqueousdispersion of modified PTFE is excellent to such an extent that thesubsequent processability, moldability and the like are notdeteriorated, and molded article excellent in heat resistance and thelike are easily obtained.

In the present disclosure, the aqueous dispersion of modified PTFE usedin coagulation stirring (hereinafter, also referred to as the dispersionof modified PTFE for coagulation) preferably has a solid concentrationof modified PTFE of 10 to 25% by mass. The solid concentration ofmodified PTFE is preferably 10 to 22% by mass, more preferably 10 to 20%by mass. In order to increase the bulk density of the modified PTFE finepowder, the concentration of the solid concentration of modified PTFE inthe aqueous dispersion of modified PTFE for coagulation is preferablyhigh. When the solid concentration of modified PTFE in the aqueousdispersion of modified PTFE for coagulation is high, the degree ofassociation of the primary modified PTFE particles increases, and theprimary modified PTFE particles are densely associated and agglomeratedto form granules. When the solid concentration of modified PTFE of theaqueous dispersion of modified PTFE for coagulation is less than 10% bymass, the agglomeration density of the primary modified PTFE particlestends to become sparse, and it is difficult to obtain the fine powder ofmodified PTFE having a high bulk density. On the other hand, if thesolid concentration of modified PTFE in the aqueous dispersion ofmodified PTFE for coagulation is too high, the concentration ofunagglomerated modified PTFE increases and the solid concentration ofunagglomerated modified PTFE in the coagulated discharge waterincreases. When the solid concentration of unagglomerated modified PTFEin the coagulated discharge water is high, the piping clogging anddischarge water treatment are costly and time-consuming. In addition,the yield of the fine powder of modified PTFE decreases. The solidconcentration of unagglomerated modified PTFE in the coagulateddischarge water is preferably low from the viewpoint of productivity ofthe fine powder of modified PTFE, more preferably less than 0.4% bymass, still more preferably less than 0.3% by mass, and particularlypreferably less than 0.2% by mass. When the solid concentration ofmodified PTFE of the aqueous dispersion of modified PTFE for coagulationexceeds 25% by mass, it is difficult to reduce the solid concentrationof unagglomerated modified PTFE of the coagulated discharge water toless than 0.4% by mass.

Since the solid concentration of modified PTFE in the aqueous dispersionof modified PTFE obtained in the step is about 10 to 45% by mass whenthe solid concentration of modified PTFE is high, a diluent such aswater is added to adjust the concentration to 10 to 25% by mass.Further, when the solid concentration of modified PTFE in the aqueousdispersion of modified PTFE after polymerization is 10 to 25% by mass,the aqueous dispersion of modified PTFE can be used as it is as theaqueous dispersion of modified PTFE for coagulation.

A pigment-containing or filler-containing powder of modified PTFE inwhich pigments and fillers are uniformly mixed can be obtained by addingpigments for coloring and various fillers for improving mechanicalproperties before or during the aggregation.

The wet powder obtained by agglomerating the modified PTFE in theaqueous dispersion is usually dried by means of vacuum, high-frequencywaves, hot air, or the like while keeping the wet powder in a state inwhich the wet powder is less fluidized, preferably in a stationarystate. Friction between the powder particles especially at hightemperature usually has unfavorable effects on the modified PTFE in theform of fine powder. This is because the particles made of such modifiedPTFE are easily formed into fibrils even with a small shearing force andlose its original, stable particulate structure. The drying is performedat a drying temperature of 10 to 300° C. (preferably 10 to 250° C.),preferably 100 to 300° C. (preferably 100 to 250° C.).

The powder of modified PTFE preferably has an average particle size(average secondary particle size) of 100 to 2,000 μm. The lower limit ofthe average secondary particle size is more preferably 200 μm or more,and still more preferably 300 μm or more. The upper limit of the averagesecondary particle size is preferably 1,000 μm or less, more preferably800 μm or less, and particularly preferably 700 μm or less. The averageparticle size is a value measured in conformity with JIS K 6891.

The powder of modified PTFE is preferable for molding, and suitableapplications include hydraulic systems such as aircraft and automobiles,fuel system tubes and the like, flexible hoses such as chemicals andsteam, and electric wire coating applications. The powder of modifiedPTFE can also be used as a binder for batteries and as a dustproofmaterial. It is also possible to produce a stretched body from thepowder of modified PTFE.

The present disclosure also provides a composition containing modifiedPTFE and a polymer (I) containing a polymerization unit (I) based on amonomer represented by the following general formula (I):

CX¹X³═CX²R(—CZ¹Z²-A⁰)_(m)  (I)

wherein X¹ and X³ are each independently F, Cl, H, or CF₃; X² is H, F,an alkyl group, or a fluorine-containing alkyl group; A⁰ is an anionicgroup; R is a linking group; Z¹ and Z² are each independently H, F, analkyl group, or a fluorine-containing alkyl group; and m is an integerof 1 or more.

X² is preferably F, Cl, H, or CF₃. Further, Z¹ and Z² are preferably For CF₃.

The modified PTFE and the polymer (I) are the same as the modified PTFEand the polymer (I) described in the production method of the presentdisclosure.

The form of the composition of the present disclosure is not limited,and may be, for example, an aqueous dispersion, a powder, a molded body,a pellet, or the like, and is preferably a powder.

Preferably, the composition of the present disclosure contains modifiedpolytetrafluoroethylene and the polymer (I) and has a content of thepolymer (I) of 0.0001% by mass or more and 20% by mass or less based onmodified polytetrafluoroethylene. In the composition of the presentdisclosure, the lower limit of the content of the polymer (I) is morepreferably 0.001% by mass, still more preferably 0.01% by mass, andfurther preferably 0.1% by mass based on modifiedpolytetrafluoroethylene. The upper limit value is more preferably 10% bymass, still more preferably 6% by mass, further preferably 4% by mass,still further preferably 2% by mass or less, particularly preferably1.5% by mass or less, and most preferably 1% by mass or less.

The content of the polymer (I) contained in the composition of thepresent disclosure can be measured by solid-state NMR.

Further, examples of the method for measuring the content of the polymer(I) include polymer measurement methods respectively described inInternational Publication No. WO 2014/099453, International PublicationNo. WO 2010/075497, International Publication No. WO 2010/075496,International Publication No. WO 2011/008381, International PublicationNo. WO 2009/055521, International Publication No. WO 1987/007619,Japanese Patent Laid-Open No. 61-293476, International Publication No.WO 2010/075494, International Publication No. WO 2010/075359,International Publication No. WO 2012/082454, International PublicationNo. WO 2006/119224, International Publication No. WO 2013/085864,International Publication No. WO 2012/082707, International PublicationNo. WO 2012/082703, International Publication No. WO 2012/082454,International Publication No. WO 2012/082451, International PublicationNo. WO 2006/135825, International Publication No. WO 2004/067588,International Publication No. WO 2009/068528, Japanese Patent Laid-OpenNo. 2004-075978, Japanese Patent Laid-Open No. 2001-226436,International Publication No. WO 1992/017635, International PublicationNo. WO 2014/069165, Japanese Patent Laid-Open No. 11-181009, and thelike.

The content of the polymer (I) in the composition can be determined by,for example, solid-state ¹⁹F-MAS NMR measurement.

Specific apparatuses may be AVANCE III HD400 manufactured by Bruker,AVANCE 300 manufactured by Bruker, and the like.

The rotational speed is set according to the resonance frequency of anapparatus, and the spinning sideband is set so as not to overlap thepeaks used to calculate the contents of the fluoropolymer and thepolymer (I).

For example, in the above composition, when the polymer (I) is acopolymer of TFE and a monomer represented by CH₂═CF(CF₂OCFCF₃COONH₄),the rotational speed may be set to be 30 kHz when using AVANCE 300manufactured by Bruker Japan in the case of determining the content ofthe copolymer of TFE and a monomer represented byCH₂═CF(CF₂OCFCF₃COONH₄) in the composition. For example, in the abovecomposition, when the polymer (I) is a copolymer of TFE and a monomerrepresented by CH₂═CF(CF₂OCFCF₃COONH₄), the content of the copolymer ofTFE and a monomer represented by CH₂═CF(CF₂OCFCF₃COONH₄) in thecomposition can be determined using the following formula from aspectrum obtained by solid-state ¹⁹F-MAS NMR measurement:

Y=(400B/(5×A+3×B))×100

Y: Content (mol %) of copolymer of TFE and monomer represented byCH₂═CF(CF₂OCFCF₃COONH₄)

A: Integral value of signal at −120 ppm

B: Sum of integral values of CF₂ and CF₃ signals at −83 ppm

The chemical shift value used was a value obtained when the peak top ofthe signal derived from the backbone of PTFE was −120 ppm.

x: Proportion (mol %) of polymerization unit based on monomerrepresented by CH₂═CF(CF₂OCFCF₃COONH₄) in copolymer of TFE and monomerrepresented by CH₂═CF(CF₂OCFCF₃COONH₄)

The content of the dimer and the trimer of the monomer represented bythe general formula (I) in the composition is preferably 1.0% by mass orless, more preferably 0.1% by mass or less, still more preferably 0.01%by mass or less, particularly preferably 0.001% by mass, and mostpreferably 0.0001% by mass or less based on the polymer (I).

The content of the dimer and the trimer of the monomer represented bythe general formula (I) in the composition can be measured by the samemethod as the method for measuring the content of the dimer and thetrimer in the polymer (I) described below.

The composition of the present disclosure preferably has a standardspecific gravity (SSG) of 2.250 or less and more preferably 2.200 orless. When the standard specific gravity is 2.250 or less, thecomposition can be stretchable, and a stretched body having excellentstretchability and excellent breaking strength can be obtained.

The standard specific gravity is preferably 2.195 or less, morepreferably 2.190 or less, and still more preferably 2.185 or less. Thelower limit of the standard specific gravity is not limited, and is, forexample, 2.130.

The standard specific gravity is determined by the water replacementmethod in conformity with ASTM D 792 using a sample molded in conformitywith ASTM D 4895-89.

The extrusion pressure of the composition of the present disclosure ispreferably 40.0 MPa or less, more preferably 35.0 MPa or less, andpreferably 5.0 MPa or more, preferably 8.0 MPa or more, and morepreferably 10.0 MPa or more. The extrusion pressure is a valuedetermined by the following method according to a method disclosed inJapanese Patent Laid-Open No. 2002-201217.

To 100 g of a powder of the composition of the present disclosure, 21.7g of a lubricant (trade name: Isopar H®, manufactured by Exxon) is addedand mixed for 3 minutes in a glass bottle at room temperature. Then, theglass bottle is left to stand at room temperature (25° C.) for at least1 hour before extrusion to obtain a lubricated resin. The lubricatedresin is paste extruded at a reduction ratio of 100:1 at roomtemperature through an orifice (diameter 2.5 mm, land length 11 mm,entrance angle 30°) into a uniform beading (beading: extruded body). Theextrusion speed, i.e. ram speed, is 20 inch/min (51 cm/min). Theextrusion pressure is a value obtained by measuring the load when theextrusion load becomes balanced in the paste extrusion and dividing themeasured load by the cross-sectional area of the cylinder used in thepaste extrusion.

The composition of the present disclosure preferably has a breakingstrength of 10.0 N or more. The breaking strength is more preferably13.0 N or more, still more preferably 16.0 N or more, and furtherpreferably 19.0 N or more. The breaking strength is preferably 20.0 N ormore, more preferably 21.0 N or more, and particularly preferably 22.0 Nor more. The higher the breaking strength, the better, but the upperlimit of the breaking strength is, for example, 50.0 N.

The breaking strength is a value determined by the following method.

First, a stretching test is performed on an extruded beading by thefollowing method to prepare a sample for measuring breaking strength.The composition of the present disclosure is heat-treated at 210° C. To100 g of the powder obtained by heat treatment, 21.7 g of a lubricant isadded and mixed for 3 minutes in a glass bottle at room temperature.Then, the glass bottle is left to stand at room temperature (25° C.) forat least 1 hour before extrusion to obtain a lubricated resin. Thelubricated resin is paste extruded at a reduction ratio of 100:1 at roomtemperature through an orifice (diameter 2.5 mm, land length 11 mm,entrance angle 30°) into a uniform beading (beading: extruded body). Theextrusion speed, i.e. ram speed, is 20 inch/min (51 cm/min).

The beading obtained by the paste extrusion is heated at 230° C. for 30minutes to remove the lubricant from the beading. Next, an appropriatelength of the beading (extruded body) is cut and clamped at each endleaving a space of 1.5 inch (38 mm) between clamps, and heated to 300°C. in an air circulation furnace. Then, the clamps were moved apart fromeach other at a desired rate (stretch rate) until the separationdistance corresponds to a desired stretch (total stretch) to perform thestretching test. This stretch method essentially followed a methoddisclosed in U.S. Pat. No. 4,576,869, except that the extrusion speed isdifferent (51 cm/min instead of 84 cm/min). “Stretch” is an increase inlength due to stretching, usually expressed as a ratio to the originallength. In the production method, the stretching rate is 1,000%/sec, andthe total stretching is 2,400%.

The stretched beading (produced by stretching the beading) obtained inthe stretching test is clamped by movable jaws having a gauge length of5.0 cm, and a tensile test is performed at 25° C. at a rate of 300mm/min, and the strength at the time of breaking is taken as thebreaking strength.

The composition of the present disclosure preferably has a stressrelaxation time of 50 seconds or more, more preferably 80 seconds ormore, and still more preferably 100 seconds or more, and the stressrelaxation time may be 150 seconds or more. The stress relaxation timeis a value measured by the following method.

Both ends of the stretched beading obtained in the stretching test aretied to a fixture to form a tightly stretched beading sample having anoverall length of 8 inches (20 cm). The fixture is placed in an oventhrough a (covered) slit on the side of the oven, while keeping the ovenat 390° C. The time it takes for the beading sample to break after it isplaced in the oven is taken as the stress relaxation time.

The composition of the present disclosure is preferably stretchable. Theterm “stretchable” as used herein is determined based on the followingcriteria.

To 100 g of PTFE powder, 21.7 g of a lubricant (trade name: Isopar H®,manufactured by Exxon) is added and mixed for 3 minutes in a glassbottle at room temperature. Then, the glass bottle is left to stand atroom temperature (25° C.) for at least 1 hour before extrusion to obtaina lubricated resin. The lubricated resin is paste extruded at areduction ratio of 100:1 at room temperature through an orifice(diameter 2.5 mm, land length 11 mm, entrance angle 30°) into a uniformbeading. The extrusion speed, i.e. ram speed, is 20 inch/min (51cm/min). The beading obtained by paste extrusion is heated at 230° C.for 30 minutes to remove the lubricant from the beading. Next, anappropriate length of the beading (extruded body) is cut and clamped ateach end leaving a space of 1.5 inch (38 mm) between clamps, and heatedto 300° C. in an air circulation furnace. Then, the clamps were movedapart from each other at a desired rate (stretch rate) until theseparation distance corresponds to a desired stretch (total stretch) toperform the stretch test. This stretch method essentially followed amethod disclosed in U.S. Pat. No. 4,576,869, except that the extrusionspeed is different (51 cm/min instead of 84 cm/min). “Stretch” is anincrease in length due to stretching, usually expressed as a ratio tothe original length. In the production method, the stretching rate is1,000%/sec, and the total stretching is 2,400%. This means that astretched beading with a uniform appearance can be obtained withoutcutting in this stretching test.

In the composition of the present disclosure, the total amount of themodified polytetrafluoroethylene and the polymer (I) is preferably 90%by mass or more, more preferably 99% by mass or more, and still morepreferably substantially 100% by mass.

In one embodiment, the composition of the present disclosure contains afluorine-containing surfactant. The composition containing afluorine-containing surfactant and PTFE has an advantage that thecomposition can be stably produced with high productivity using afluorine-containing surfactant. The composition of the presentdisclosure is preferably substantially free from a fluorine-containingsurfactant. The expression “substantially free from afluorine-containing surfactant” as used herein means that the amount ofthe fluorine-containing surfactant is 10 mass ppm or less based onmodified polytetrafluoroethylene. The content of the fluorine-containingsurfactant is preferably 1 mass ppm or less, more preferably 100 massppb or less, still more preferably 10 mass ppb or less, furtherpreferably 1 mass ppb or less, and particularly preferably thefluorine-containing surfactant is below the detection limit as measuredby liquid chromatography-mass spectrometry (LC/MS/MS). The amount of thefluorine-containing surfactant can be determined by a known method. Forexample, it can be determined by LC/MS/MS analysis. First, the resultingaqueous dispersion, powder, molded body or pellet, or modifiedpolytetrafluoroethylene obtained by finely dividing a molded body ormodified polytetrafluoroethylene obtained by finely dividing a pellet isextracted into an organic solvent of methanol, and the extract liquid issubjected to LC/MS/MS analysis. Then, the molecular weight informationis extracted from the LC/MS/MS spectrum to confirm agreement with thestructural formula of the candidate surfactant.

Thereafter, aqueous solutions having five or more differentconcentration levels of the confirmed surfactant are prepared, andLC/MS/MS analysis is performed for each concentration level to prepare acalibration curve with the area.

The resulting aqueous dispersion or powder or a powder obtained bycrushing the molded body is subjected to Soxhlet extraction withmethanol, and the extracted liquid is subjected to LC/MS/MS analysis forquantitative measurement.

In other words, the content of the fluorine-containing surfactant can bequantified by LC/MS/MS analysis.

First, extraction is performed by adding methanol to the composition,and the obtained extracted liquid is subjected to LC/MS/MS analysis. Inorder to further improve the extraction efficiency, treatment by Soxhletextraction, ultrasonic treatment or the like may be performed.

From the obtained LC/MS/MS spectrum, the molecular weight information isextracted to confirm agreement with the structural formula of thecandidate fluorine-containing surfactant.

Thereafter, aqueous solutions having five or more different contentlevels of the confirmed fluorine-containing surfactant are prepared, andLC/MS/MS analysis of the aqueous solution of each content is performed,and the relationship between the content and the area for the content isplotted, and a calibration curve is drawn.

Then, using the calibration curve, the area of the LC/MS/MS chromatogramof the fluorine-containing surfactant in the extract can be convertedinto the content of the fluorine-containing surfactant.

The fluorine-containing surfactant is the same as those exemplified inthe production method of the present disclosure. For example, thesurfactant may be a fluorine atom-containing surfactant having, in theportion excluding the anionic group, 20 or less carbon atoms in total,may be a fluorine-containing surfactant having an anionic moiety havinga molecular weight of 800 or less, and may be a fluorine-containingsurfactant having a Log POW of 3.5 or less.

Examples of the anionic fluorine-containing surfactant include compoundsrepresented by the general formula (N⁰), and specific examples thereofinclude compounds represented by the general formula (N¹), compoundsrepresented by the general formula (N²), compounds represented by thegeneral formula (N³), compounds represented by the general formula (N⁴),and compounds represented by the general formula (N⁵). More specificexamples thereof include a perfluorocarboxylic acid (I) represented bythe general formula (I), an ω-H perfluorocarboxylic acid (II)represented by the general formula (II), a perfluoropolyethercarboxylicacid (III) represented by the general formula (III), aperfluoroalkylalkylenecarboxylic acid (IV) represented by the generalformula (IV), a perfluoroalkoxyfluorocarboxylic acid (V) represented bythe general formula (V), a perfluoroalkylsulfonic acid (VI) representedby the general formula (VI), an ω-H perfluorosulfonic acid (VII)represented by the general formula (VII), a perfluoroalkylalkylenesulfonic acid (VIII) represented by the general formula (VIII), analkylalkylene carboxylic acid (IX) represented by the general formula(IX), a fluorocarboxylic acid (X) represented by the general formula(X), an alkoxyfluorosulfonic acid (XI) represented by the generalformula (XI), a compound (XII) represented by the general formula (XII),and a compound (XII) represented by the following general formula(XIII).

The composition of the present disclosure can be obtained by theproduction method of the present disclosure described above. Further,the composition satisfying the above breaking strength, stressrelaxation time, standard specific gravity, and extrusion pressure canbe obtained by a production method comprising polymerizingtetrafluoroethylene and a modifying monomer in an aqueous medium in thepresence of a polymer (I) containing a polymerization unit (I) based ona monomer represented by the general formula (I) to obtain modifiedpolytetrafluoroethylene (hereinafter also referred to as a“polymerization step”) and adding a polymerization terminator to theaqueous medium (hereinafter also referred to as a “polymerizationterminator adding step”).

The present disclosure also provides a stretched body obtained bystretching the above composition. Stretching is not limited, andconventionally known methods and conditions for stretching PTFE can beemployed.

The present disclosure further provides a stretched body containingmodified polytetrafluoroethylene and a polymer (I) containing apolymerization unit (I) based on a monomer represented by the followinggeneral formula (I):

CX¹X³═CX²R(—CZ¹Z²-A⁰)_(m)  (I)

wherein X¹ and X³ are each independently F, Cl, H, or CF₃; X² is H, F,an alkyl group, or a fluorine-containing alkyl group; A⁰ is an anionicgroup; R is a linking group; Z¹ and Z² are each independently H, F, analkyl group, or a fluorine-containing alkyl group; and m is an integerof 1 or more.

X² is preferably F, Cl, H, or CF₃. Further, Z¹ and Z² are preferably For CF₃.

The anionic group (A⁰) is preferably an anionic group that is a sulfategroup, a carboxylate group, a phosphate group, a phosphonate group, asulfonate group, or —C(CF₃)₂OM wherein M is —H, a metal atom, —NR⁷ ₄,imidazolium optionally having a substituent, pyridinium optionallyhaving a substituent, or phosphonium optionally having a substituent,and R⁷ is H or an organic group.

In the stretched body of the present disclosure, the modifiedpolytetrafluoroethylene and the polymer (I) are the same as thosedescribed with respect to the composition of the present disclosure, andrespective suitable embodiments can be adopted.

The stretched body of the present disclosure preferably has a breakingstrength of 10.0 N or more, more preferably 13.0 N or more, still morepreferably 16.0 N or more, and further preferably 19.0 N or more.

The higher the breaking strength, the better, but the upper limit of thebreaking strength is, for example, 50.0 N.

Concerning the breaking strength of the stretched body, the stretchedbody is clamped by movable jaws having a gauge length of 5.0 cm, and atensile test is performed at 25° C. at a rate of 300 mm/min, and thestrength at the time of breaking is taken as the breaking strength.

The stretched body of the present disclosure preferably has a stressrelaxation time of 50 seconds or more, more preferably 80 seconds ormore, and still more preferably 100 seconds or more, and the stressrelaxation time may be 150 seconds or more. The stress relaxation timeis a value measured by the following method.

Concerning the stress relaxation time of the stretched body, both endsof the stretched body are tied to a fixture to form a tightly stretchedbeading sample having an overall length of 8 inches (20 cm), and thefixture is placed in an oven through a (covered) slit on the side of theoven, while keeping the oven at 390° C. The time it takes for the sampleto break after it is placed in the oven is taken as the stressrelaxation time.

The stretched body of the present disclosure preferably has anendothermic peak temperature between 325 and 350° C. Further, thestretched body of the present disclosure preferably has an endothermicpeak temperature between 325 and 350° C. and between 360 and 390° C. Theendothermic peak temperature is a temperature corresponding to themaximum value in the heat-of-fusion curve when the stretched body isheated at a rate of 10° C./min using a differential scanning calorimeter(DSC).

The stretched body of the present disclosure preferably has a porosityin the range of 50% to 99%. The porosity is preferably 60% or more, morepreferably 70% or more. Too small proportion of PTFE in the stretchedbody may result in insufficient strength of the stretched body, so theporosity is preferably 95% or less, and more preferably 90% or less.

The porosity of the stretched body can be calculated from the followingformula using the apparent density p.

Porosity (%)=[(2.2−φ/2.2]×100

In the formula, 2.2 is the true density (g/cm³) of PTFE.

Regarding the density p of the stretched body, when the stretched bodyis in the form of a film or a sheet, a mass of the sample cut into aspecific size is measured by a precision scale, and the density of thesample is calculated from the measured mass and the film thickness ofthe sample by the following formula.

ρ=M/(4.0×12.0×t)

ρ=density (film density) (g/cm³)

M=mass (g)

t=film thickness (cm)

The measurement and calculation are performed at three points, and theaverage value thereof is taken as the film density.

As for the film thickness, five stretched bodies are stacked and thetotal film thickness is measured using a film thickness meter, and thevalue obtained by dividing the value by five is taken as the thicknessof one film.

Regarding the density p of the stretched body, when the stretched bodyhas a cylindrical shape, a mass of the sample cut into a certain lengthis measured by a precision scale, and the density of the sample iscalculated from the measured mass and the outer diameter of the sampleby the following formula.

ρ=M/(r×r×π)×L

ρ=density (g/cm³)

M=mass (g)

r=radius (cm)

L=length (cm)

π=pi

The outer diameter of the stretched body is measured using a laserdisplacement sensor. The radius is the value obtained by dividing thevalue by 2.

The above measurement and calculation are performed at three points, andthe average value thereof is taken as the density.

The stretched body of the present disclosure preferably has a content ofthe polymer (I) of 0.0001% by mass or more and 20% by mass or less basedon polytetrafluoroethylene. In the stretched body of the presentdisclosure, the lower limit of the content of the polymer (I) is morepreferably 0.001% by mass, still more preferably 0.01% by mass, andparticularly preferably 0.1% by mass based on polytetrafluoroethylene.The upper limit value is more preferably 10% by mass, still morepreferably 6% by mass, further preferably 4% by mass, still furtherpreferably 2% by mass or less, particularly preferably 1.5% by mass orless, and most preferably 1% by mass or less.

The content of the polymer (I) can be determined by solid-state NMRmeasurement.

The stretched body of the present disclosure is preferably substantiallyfree from a fluorine-containing surfactant. In the present disclosure,the expression “substantially free from a fluorine-containingsurfactant” means that the amount of the fluorine-containing surfactantis 10 mass ppm or less based on modified polytetrafluoroethylene. Thecontent of the fluorine-containing surfactant is preferably 1 mass ppmor less, more preferably 100 mass ppb or less, still more preferably 10mass ppb or less, further preferably 1 mass ppb or less, andparticularly preferably the fluorine-containing surfactant is below thedetection limit as measured by liquid chromatography-mass spectrometry(LC/MS/MS).

The amount of the fluorine-containing surfactant can be determined by aknown method. For example, it can be determined by LC/MS/MS analysis.First, a finely divided stretched body is extracted into an organicsolvent of methanol, and the extract liquid is subjected to LC/MS/MSanalysis. Then, the molecular weight information is extracted from theLC/MS/MS spectrum to confirm agreement with the structural formula ofthe candidate surfactant.

Thereafter, aqueous solutions having five or more differentconcentration levels of the confirmed surfactant are prepared, andLC/MS/MS analysis is performed for each concentration level to prepare acalibration curve with the area.

The resulting powder obtained by crushing the stretched body issubjected to Soxhlet extraction with methanol, and the extracted liquidis subjected to LC/MS/MS analysis for quantitative measurement.

In other words, the content of the fluorine-containing surfactant can bequantified by LC/MS/MS analysis.

First, extraction is performed by adding methanol to the finely dividedstretched body, and the obtained extracted liquid is subjected toLC/MS/MS analysis. In order to further improve the extractionefficiency, treatment by Soxhlet extraction, ultrasonic treatment or thelike may be performed.

From the obtained LC/MS/MS spectrum, the molecular weight information isextracted to confirm agreement with the structural formula of thecandidate fluorine-containing surfactant.

Thereafter, aqueous solutions having five or more different contentlevels of the confirmed fluorine-containing surfactant are prepared, andLC/MS/MS analysis of the aqueous solution of each content is performed,and the relationship between the content and the area for the content isplotted, and a calibration curve is drawn.

Then, using the calibration curve, the area of the LC/MS/MS chromatogramof the fluorine-containing surfactant in the extract can be convertedinto the content of the fluorine-containing surfactant.

The fluorine-containing surfactant is the same as those exemplified inthe production method of the present disclosure. For example, thesurfactant may be a fluorine atom-containing surfactant having, in theportion excluding the anionic group, 20 or less carbon atoms in total,may be a fluorine-containing surfactant having an anionic moiety havinga molecular weight of 800 or less, and may be a fluorine-containingsurfactant having a Log POW of 3.5 or less.

Examples of the anionic fluorine-containing surfactant include compoundsrepresented by the general formula (N⁰), and specific examples thereofinclude compounds represented by the general formula (N¹), compoundsrepresented by the general formula (N²), compounds represented by thegeneral formula (N³), compounds represented by the general formula (N⁴),and compounds represented by the general formula (N⁵). More specificexamples thereof include a perfluorocarboxylic acid (I) represented bythe general formula (I), an ω-H perfluorocarboxylic acid (II)represented by the general formula (II), a perfluoropolyethercarboxylicacid (III) represented by the general formula (III), aperfluoroalkylalkylenecarboxylic acid (IV) represented by the generalformula (IV), a perfluoroalkoxyfluorocarboxylic acid (V) represented bythe general formula (V), a perfluoroalkylsulfonic acid (VI) representedby the general formula (VI), an ω-H perfluorosulfonic acid (VII)represented by the general formula (VII), a perfluoroalkylalkylenesulfonic acid (VIII) represented by the general formula (VIII), analkylalkylene carboxylic acid (IX) represented by the general formula(IX), a fluorocarboxylic acid (X) represented by the general formula(X), an alkoxyfluorosulfonic acid (XI) represented by the generalformula (XI), a compound (XII) represented by the general formula (XII),and a compound (XII) represented by the following general formula(XIII).

The stretched body of the present disclosure can be obtained bystretching the composition of the present disclosure.

The stretched body of the present disclosure is also preferably in theform of a film, a tube, fibers, or rods.

When the stretched body of the present disclosure is a film (stretchedfilm or porous film), the stretched body can be formed by stretching bya known PTFE stretching method.

Preferably, roll-stretching a sheet-shaped or rod-shaped paste extrudatein an extruding direction can provide a uniaxially stretched film.

Further stretching in a transverse direction using a tenter, forexample, can provide a biaxially stretched film.

Semi-sintering treatment is also preferably performed before stretching.

As the stretching conditions, a speed of 5 to 2,000%/sec and a stretchratio of 200% or more are preferably employed.

The stretched body of the present disclosure is a porous body having ahigh porosity, and can suitably be used as a filter material for avariety of microfiltration filters such as air filters and chemicalfilters and a support member for polymer electrolyte films. Thestretched body is also useful as a material of products used in thefields of textiles, of medical treatment, of electrochemistry, ofsealants, of air filters, of ventilation/internal pressure adjustment,of liquid filters, and of consumer goods.

The following provides examples of specific applications.

Electrochemical Field

Examples of the applications in this field include prepregs fordielectric materials, EMI-shielding materials, and heat conductivematerials. More specifically, examples thereof include printed circuitboards, electromagnetic interference shielding materials, insulatingheat conductive materials, and insulating materials.

Sealant Field

Examples of the applications in this field include gaskets, packings,pump diaphragms, pump tubes, and sealants for aircraft.

Air Filter Field

Examples of the applications in this field include ULPA filters (forproduction of semiconductors), HEPA filters (for hospitals and forproduction of semiconductors), cylindrical cartridge filters (forindustries), bag filters (for industries), heat-resistant bag filters(for exhaust gas treatment), heat-resistant pleated filters (for exhaustgas treatment), SINBRAN filters (for industries), catalyst filters (forexhaust gas treatment), adsorbent-attached filters (for HDD embedment),adsorbent-attached vent filters (for HDD embedment), vent filters (forHDD embedment, for example), filters for cleaners (for cleaners),general-purpose multilayer felt materials, cartridge filters for GT (forinterchangeable items for GT), and cooling filters (for housings ofelectronic devices).

Ventilation/Internal Pressure Adjustment Field

Examples of the applications in this field include materials for freezedrying such as vessels for freeze drying, ventilation materials forautomobiles for electronic circuits and lamps, applications relating tovessels such as vessel caps, protective ventilation for electronicdevices, including small devices such as tablet terminals and mobilephone terminals, and ventilation for medical treatment.

Liquid Filter Field

Examples of the applications in this field include liquid filters forsemiconductors (for production of semiconductors), hydrophilic PTFEfilters (for production of semiconductors), filters for chemicals (forliquid chemical treatment), filters for pure water production lines (forproduction of pure water), and back-washing liquid filters (fortreatment of industrial discharge water).

Consumer Goods Field

Examples of the applications in this field include clothes, cable guides(movable wires for motorcycles), clothes for motor cyclists, cast liners(medical supporters), filters for cleaners, bagpipes (musicalinstrument), cables (signal cables for guitars, etc.), and strings (forstring instrument).

Textile Field

Examples of the applications in this field include PTFE fibers (fibermaterials), machine threads (textiles), weaving yarns (textiles), andropes.

Medical Treatment Field

Examples of the applications in this field include implants (stretchedarticles), artificial blood vessels, catheters, general surgicaloperations (tissue reinforcing materials), products for head and neck(dura mater alternatives), oral health (tissue regenerative medicine),and orthopedics (bandages).

Although the embodiments have been described above, it will beunderstood that various changes in form and details are possible withoutdeparting from the gist and scope of the claims.

EXAMPLES

The present disclosure is described with reference to examples, but thepresent disclosure is not intended to be limited by these examples.

The numerical values of the Examples were measured by the followingmethods.

Average Primary Particle Size

An aqueous dispersion of a fluoropolymer was diluted with water to asolid concentration of 0.15% by mass. The transmittance of incidentlight at 550 nm relative to the unit length of the resulting dilutedlatex was determined and the number-based length average primaryparticle size was determined by measuring the Feret diameter with atransmission electron microscope image. Based on these values, acalibration curve was drawn. Using this calibration curve, the averageprimary particle size was determined from the measured transmittance ofthe projected light at 550 nm of each sample.

Also, the average primary particle size can be determined by dynamiclight scattering. In dynamic light scattering, the average primaryparticle size was determined by preparing an aqueous dispersion of afluoropolymer adjusted to a solid concentration of about 1.0% by mass,and ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) at 25° C.with 70 accumulations. The refractive index of the solvent (water) was1.3328, and the viscosity of the solvent (water) was 0.8878 mPa·s.

Standard Specific Gravity (SSG)

Using a sample molded in conformity with ASTM D 4895-89, the SSG wasdetermined by the water replacement method in conformity with ASTM D792.

Endothermic peak temperature Regarding each of the PTFE powders obtainedin Examples, a heat-of-fusion curve was drawn at atemperature-increasing rate of 10° C./min using a differential scanningcalorimeter (DSC), and the temperature corresponding to the maximumvalue of the endothermic peak in the heat-of-fusion curve was taken asthe endothermic peak temperature of PTFE.

Content of Modifying Monomer Unit

The content of the HFP unit was determined from the infrared absorbanceobtained by producing a thin film disk by press molding the PTFE powderand carrying out FT-IR measurement, in which the ratio of the absorbanceat 935 cm⁻¹/the absorbance at 982 cm⁻¹ was multiplied by 0.3.

The content of the PMVE unit was determined using the following formulafrom a spectrum obtained by solid-state ¹⁹F-MAS NMR measurement:

X=(4B/3)/(A+(B/3))×100

X: Content (mol %) of PMVE unit

A: Integral value of signal at −120 ppm

B: Integral value of CF signal at −52 ppm

The chemical shift value used was a value obtained when the peak top ofthe signal derived from the backbone of PTFE was −120 ppm.

The content of the CH₂═CF(CF₂OCFCF₃COONH₄) (modifying monomer a) unitwas derived from the amount of the entirety of the modifying monomer acharged.

Fluoropolymer Solid Concentration

In an air dryer, 1 g of an aqueous dispersion of a fluoropolymer wasdried at 150° C. for 60 minutes, and the ratio of the mass of thenon-volatile matter to the mass of the aqueous dispersion (1 g) wasexpressed in percentage and taken as the solid concentration thereof.

Content of Polymer A and Polymer D

The content of polymer A contained in PTFE powder was determined usingthe following formula from a spectrum obtained by solid-state ¹⁹F-MASNMR measurement:

Y=(4B/(5A+3B))×100

Y: Content (mol %) of polymer A or polymer D

A: Integral value of signal at −120 ppm

B: Sum of integral values of CF₂ and CF₃ signals at −83 ppm

The chemical shift value used was a value obtained when the peak top ofthe signal derived from the backbone of PTFE was −120 ppm.

Content of Polymer B

The content of polymer B contained in PTFE powder was determined usingthe following formula from a spectrum obtained by solid-state ¹⁹F-MASNMR measurement:

Y=(4B/(10A+3B))×100

Y: Content (mol %) of polymer B

A: Integral value of signal at −120 ppm

B: Sum of integral values of CF₂ and CF₃ signals at −81 and −83 ppm

The chemical shift value used was a value obtained when the peak top ofthe signal derived from the backbone of PTFE was −120 ppm.

Content of Polymer C

The content of polymer C contained in PTFE powder was determined usingthe following formula from a spectrum obtained by solid-state ¹⁹F-MASNMR measurement:

Y=(4B/(4.62A+2.77B))×100

Y: Content (mol %) of polymer C

A: Integral value of signal at −120 ppm

B: Sum of integral values of CF₂ and CF₃ signals at −83 ppm

The chemical shift value used was a value obtained when the peak top ofthe signal derived from the backbone of PTFE was −120 ppm.

Content of Polymer E

The content of polymer E contained in PTFE powder was determined from aspectrum obtained by solid-state ¹⁹F-MAS NMR measurement.

Content of Polymer F

The content of polymer F contained in PTFE powder was determined from aspectrum obtained by solid-state ¹⁹F-MAS NMR measurement.

Measurement of Extrusion Pressure

To 100 g of fine powder, 21.7 g of a lubricant (trade name: Isopar H®,manufactured by Exxon) is added and mixed for 3 minutes in a glassbottle at room temperature. Then, the glass bottle is left to stand atroom temperature (25° C.) for at least 1 hour before extrusion to obtaina lubricated resin. The lubricated resin is paste-extruded at areduction ratio of 100:1 at room temperature through an orifice(diameter 2.5 mm, land length 11 mm, entrance angle 30°) into a uniformbeading (beading: extruded body). The extrusion speed, i.e., ram speed,is 20 inch/min (51 cm/min). The value obtained by measuring the loadwhen the extrusion load became balanced in the paste extrusion anddividing the measured load by the cross-sectional area of the cylinderused in the paste extrusion is taken as the extrusion pressure.

Stretching Test

The beading obtained by the above paste extrusion is heated at 230° C.for 30 minutes to remove the lubricant from the beading. Next, anappropriate length of the beading (extruded body) is cut and clamped ateach end leaving a space of 1.5 inch (38 mm) between clamps, and heatedto 300° C. in an air circulation furnace. Then, the clamps were movedapart from each other at a desired rate (stretch rate) until theseparation distance corresponds to a desired stretch (total stretch) toperform the stretch test. This stretch method essentially followed amethod disclosed in U.S. Pat. No. 4,576,869, except that the extrusionspeed is different (51 cm/min instead of 84 cm/min). “Stretch” is anincrease in length due to stretching, usually expressed as a ratio tothe original length. In the production method, the stretching rate was1,000%/sec, and the total stretching was 2,400%.

Breaking Strength

The stretched beading obtained in the stretching test (produced bystretching the beading) is clamped by movable jaws having a gauge lengthof 5.0 cm, and a tensile test is performed at 25° C. at a rate of 300mm/min, and the strength at the time of breaking is determined as thebreaking strength.

Stress Relaxation Time

Both ends of the stretched beading obtained in the stretching test aretied to a fixture to form a tightly stretched beading sample having anoverall length of 8 inches (20 cm). The fixture is placed in an oventhrough a (covered) slit on the side of the oven, while keeping the ovenat 390° C. The time it takes for the beading sample to break after itwas placed in the oven is determined as the stress relaxation time.

Appearance of Stretched Body

The appearance of the stretched beading (those produced by stretchingthe beadings) obtained in the stretching test was visually observed.

Uniform: Appearance of stretched beading was uniform.

Non-uniform: Appearance of stretched beading was not uniform, e.g.,cracking, swelling, and coarseness and fineness were observed in thestretched beading.

Aspect Ratio

The aspect ratio was determined by observing the aqueous dispersion ofPTFE diluted to have a solid concentration of about 1% by mass with ascanning electron microscope (SEM), performing image processing on 400or more particles selected at random, and averaging the ratios of themajor axis to the minor axis.

Method for measuring contents of dimers and trimers of monomers (such asmonomers D, E, and F) in polymers (such as polymers D, E, and F).

(1) Extraction from Aqueous Solution

The solid content of an aqueous solution of a polymer was measured, andthe amount of the aqueous solution corresponding to 0.2 g of the solidcontent of the polymer was weighed. Thereafter, water and methanol wereadded such that the volume ratio of water, including the water containedin the aqueous solution, to methanol was 50/50 (vol %) to obtain a mixedsolution containing the polymer, water, and methanol. Thereafter, theobtained mixed solution was centrifuged at 4,000 rpm for 1 hour, and thesupernatant containing the polymer was recovered as an extract.

The extract was analyzed using a liquid chromatograph-mass spectrometer(Waters, LC-MS ACQUITY UPLC/TQD) to obtain a chromatogram of theextract.

The content of a dimer and a trimer of a monomer contained in theextract was obtained by converting the integral values of peaks derivedfrom the dimer and the trimer of the monomer appearing in thechromatogram of the extract into the contents of the dimer and thetrimer of the monomer using a calibration curve.

(2) Calibration Curve of Monomer

Five concentration levels of a methanol standard solution of a monomerhaving a known content of 1 ng/mL to 100 ng/mL were prepared, andmeasurement was made using a liquid chromatograph-mass spectrometer(Waters, LC-MS ACQUITY UPLC/TQD). The relationship between the contentof each monomer and the integrated value of a peak corresponding to thecontent was plotted to create a calibration curve (first-orderapproximation) of each monomer. Next, the calibration curve (first-orderapproximation) of each monomer was used to create calibration curves ofa dimer and a trimer of each monomer.

Measuring Instrument Configuration and LC-MS Measurement Conditions

[Table 1]

TABLE 1 LC unit Equipment Acquity UPLC manufactured by Waters ColumnAcquity UPLC BEH C18 1.7 mm (2.1 × 50 mm) manufactured by Waters Mobilephase A CH₃CN B 20 mM CH₃COONH4/H₂O 0→4.5 mm A:B = 10:90 1.5→8.5 min A:B= 10:90 → A:B = 90:10 Linear gradient 8.5→10 min A:B = 90:10 Flow rate0.4 mL/min Column temperature 40° C. Sample injection amo

5 μL MS unit Equipment TQ Detecter Measurement mode MRM(MultipleReaction Monitoring) Ionization method Electrospray ionization SCAN

indicates data missing or illegible when filed

The quantification limit in this treasuring instrument configuration is1 ng/mL.

In the Examples, a homopolymer (a number average molecular weight of90,000 and a weight average molecular weight of 190,000) (hereinafterreferred to as a “polymer A”) of a monomer represented by the followingformula:

CH₂═CF(CF₂OCFCF₃COONH₄)

(hereinafter referred to as a “modifying monomer a”) was used.

The number average molecular weight and the weight average molecularweight of the polymer were measured by gel permeation chromatography(GPC) using GPC HLC-8020 manufactured by Tosoh Corporation and columnsmanufactured by Showa Denko K.K. (one GPC KF-801, one GPC KF-802, andtwo GPC KF-806M connected in series) while allowing tetrahydrofuran(THF) to flow as a solvent at a flow rate of 1 ml/min, and the molecularweights were calculated using monodisperse polystyrene as a standard.

Example 1

To a reactor made of SUS with an internal volume of 6 L and equippedwith a stirrer, 3,560 g of deionized water, 104 g of paraffin wax, 3.58g of the polymer A, and 51.6 mg of the modifying monomer a were added.Aqueous ammonia was added to adjust the pH to 9.0. Next, the contents ofthe reactor were suctioned while being heated to 70° C., and, at thesame time, the reactor was purged with TFE to remove oxygen in thereactor, and the contents were stirred. After 0.8 g of HFP was added tothe reactor, TFE was added until the pressure was 0.73 MPaG. Then, 17.9mg of an anonium persulfate (APS) initiator dissolved in 20 g ofdeionized water was added to the reactor such that the pressure of thereactor was 0.83 MPaG. After the initiator was added, the pressuredropped, and the initiation of polymerization was observed. TFE wasadded to the reactor to maintain a constant pressure of 0.78 MPaG. WhenTFE consumed in the reaction reached about 180 g, the supply of TFE andstirring were stopped. Subsequently, the gas in the reactor was slowlyreleased until the pressure of the reactor reached 0.02 MPaG.Thereafter, TFE was supplied until the pressure of the reactor was 0.78MPaG, and stirring was started again to continue the reaction. When TFEconsumed in the reaction reached about 900 g, the supply of TFE wasstopped, stirring was stopped, and the reaction was terminated.Thereafter, the reactor was evacuated until the pressure in the reactorreached normal pressure, and the contents were taken out from thereactor and cooled. The supernatant paraffin wax was removed from theaqueous dispersion of PTFE. The solid content of the resulting aqueousdispersion of PTFE was 20.7% by mass, and the average primary particlesize was 218 nm. The resulting aqueous dispersion of PTFE was dilutedwith deionized water to have a solid content of about 10% by mass andcoagulated under a high-speed stirring condition. The coagulated wetpowder was dried at 210° C. for 18 hours. Various physical properties ofthe resulting PTFE powder were measured. The results are shown in thetables.

Example 2

Polymerization was performed in the same manner as in Example 1 exceptthat unlike in Example 1, the modifying monomer a was used in an amountof 6.4 mg instead of 51.6 mg, and PMVE was used in place of HFP. Thesolid content of the resulting aqueous dispersion of PTFE was 20.4% bymass, and the average primary particle size was 227 nm. Various physicalproperties of the resulting PTFE powder were measured. The results areshown in the tables.

Example 3

Polymerization was performed in the same manner as in Example 1 exceptthat unlike in Example 1, the polymer A was used in an amount of 5.37 ginstead of 3.58 g, the modifying monomer a was used in an amount of 430mg instead of 51.6 mg, and the supply of TFE was stopped when the amountof TFE consumed in the reaction reached about 1,250 g. The solid contentof the resulting aqueous dispersion of PTFE was 26.1% by mass, and theaverage primary particle size was 227 nm. Various physical properties ofthe resulting PTFE powder were measured. The results are shown in thetables.

Example 4

Polymerization was performed in the same manner as in Example 1 exceptthat unlike in Example 1, the modifying monomer a was used in an amountof 6.4 mg instead of 51.6 mg, and 1.8 mg of polyoxyethylene(10)octylphenyl ether was added. The solid content of the resulting aqueousdispersion of PTFE was 20.3% by mass, and the average primary particlesize was 227 nm. Various physical properties of the resulting PTFEpowder were measured. The results are shown in the tables.

Example 5

To a reactor made of SUS with an internal volume of 3 L and equippedwith a stirrer, 1,800 g of deionized water, 90 g of paraffin wax, 1.80 gof the polymer A, and 25.9 mg of the modifying monomer a were added.Aqueous ammonia was added to adjust the pH to 9.1. Then, the contents ofthe reactor were suctioned while being heated to 80° C., and, at thesame time, the reactor was purged with TFE to remove oxygen in thereactor, and the contents were stirred. After 1.26 g of HFP was added tothe reactor, TFE was added until the pressure was 1.50 MPaG. Then, 9.0mg of an ammonium persulfate (APS) initiator was added to the reactor.After the initiator was added, the pressure dropped, and the initiationof polymerization was observed. TFE was added to the reactor to maintaina constant pressure of 1.50 MPaG. When TFE consumed in the reactionreached about 510 g, the supply of TFE was stopped, stirring wasstopped, and the reaction was terminated. Thereafter, the reactor wasevacuated until the pressure in the reactor reached normal pressure, andthe contents were taken out from the reactor and cooled. The supernatantparaffin wax was removed from the aqueous dispersion of PTFE. The solidcontent of the resulting aqueous dispersion of PTFE was 23.5% by mass,and the average primary particle size was 202 nm. The resulting aqueousdispersion of PTFE was diluted with deionized water to have a solidcontent of about 10% by mass and coagulated under a high-speed stirringcondition. The coagulated wet powder was dried at 180° C. for 18 hours.Various physical properties of the resulting PTFE powder were measured.The results are shown in the tables.

Example 6

Polymerization was performed in the same manner as in Example 1 exceptthat unlike in Example 1, HFP was not added, and the operation when TFEconsumed in the reaction reached about 180 g was not performed. Thesolid content of the resulting aqueous dispersion of PTFE was 20.1% bymass, and the average primary particle size was 277 nm. Various physicalproperties of the resulting PTFE powder were measured. The results areshown in the tables.

Example 7

To a reactor made of SUS with an internal volume of 6 L and equippedwith a stirrer, 3,600 g of deionized water, 180 g of paraffin wax, 7.20g of the polymer A, and 104 mg of the modifying monomer a were added.Aqueous ammonia was added to adjust the pH to 9.1. Next, the contents ofthe reactor were suctioned while being heated to 85° C., and, at thesame time, the reactor was purged with TFE to remove oxygen in thereactor, and the contents were stirred. TFE was added until the pressurewas 2.70 MPaG. Then, 56 mg of ammonium persulfate (APS) and 289 mg ofdisuccinic acid peroxide (DSP) serving as polymerization initiators werecharged. The initiators were added to the reactor. After the initiatorswere added, the pressure dropped, and the initiation of polymerizationwas observed. TFE was added to the reactor to maintain a constantpressure of 2.70 MPaG. When TFE consumed in the reaction reached about900 g, the supply of TFE was stopped, stirring was stopped, and thereaction was terminated. Thereafter, the reactor was evacuated until thepressure in the reactor reached normal pressure, and the contents weretaken out from the reactor and cooled. The supernatant paraffin wax wasremoved from the aqueous dispersion of PTFE. The solid content of theresulting aqueous dispersion of PTFE was 21.0% by mass, and the averageprimary particle size was 197 nm. The resulting aqueous dispersion ofPTFE was diluted with deionized water to have a solid content of about10% by mass and coagulated under a high-speed stirring condition. Thecoagulated wet powder was dried at 180° C. for 18 hours. Variousphysical properties of the resulting PTFE powder were measured. Theresults are shown in the tables.

Example 8

To a reactor made of glass with an internal volume of 1 L and equippedwith a stirrer, 530 g of deionized water, 30 g of paraffin wax, and 0.52g of the polymer A were added, and aqueous ammonia was added to adjustthe pH to 9.2. Next, the contents of the reactor were suctioned whilebeing heated to 70° C., and, at the same time, the reactor was purgedwith a TFE monomer to remove oxygen in the reactor. Thereafter, thecontents were stirred at 540 rpm. After 0.18 g of HFP was added to thereactor, a TFE monomer was added until the pressure was 0.73 MPaG. Then,2.75 mg of an ammonium persulfate (APS) initiator dissolved in 20 g ofdeionized water was added to the reactor such that the pressure of thereactor was 0.83 MPaG. After the initiator was added, the pressuredropped, and the initiation of polymerization was observed. The TFEmonomer was added to the reactor to maintain pressure, andpolymerization was continued until about 140 g of the TFE monomerreacted. Thereafter, the reactor was evacuated until the pressure in thereactor reached normal pressure, and the contents were taken out fromthe reactor and cooled. The supernatant paraffin wax was removed fromthe aqueous dispersion of PTFE.

The solid content of the resulting aqueous dispersion of PTFE was 21.5%by mass, and the average primary particle size was 211 nm.

The resulting aqueous dispersion of PTFE was diluted with deionizedwater to have a solid concentration of about 10% by mass and coagulatedunder a high-speed stirring condition. The coagulated wet powder wasdried at 150° C. for 18 hours. Various physical properties of theresulting PTFE powder were measured. The results are shown in thetables.

Example 9

To a reactor made of glass with an internal volume of 1 L and equippedwith a stirrer, 530 g of deionized water, 30 g of paraffin wax, and 0.55g of a polymer B that is a homopolymer (a weight average molecularweight of 9.7×10⁴ and a number average molecular weight of 3.3×10⁴) of amonomer represented by CH₂═CF(CF₂OCFCF₃CF₂OCFCF₃COONH₄) were added, andaqueous ammonia was added to adjust the pH to 9.2. Next, the contents ofthe reactor were suctioned while being heated to 70° C., and, at thesame time, the reactor was purged with a TFE monomer to remove oxygen inthe reactor. Thereafter, the contents were stirred at 540 rpm. After0.13 g of PMVE was added to the reactor, the TFE monomer was added untilthe pressure was 0.73 MPaG. Then, 2.75 mg of an ammonium persulfate(APS) initiator dissolved in 20 g of deionized water was added to thereactor such that the pressure of the reactor was 0.83 MPaG. After theinitiator was added, the pressure dropped, and the initiation ofpolymerization was observed. The TFE monomer was added to the reactor tomaintain pressure, and polymerization was continued until about 140 g ofthe TFE monomer reacted. Thereafter, the reactor was evacuated until thepressure in the reactor reached normal pressure, and the contents weretaken out from the reactor and cooled. The supernatant paraffin wax wasremoved from the aqueous dispersion of PTFE.

The solid content of the resulting aqueous dispersion of PTFE was 21.5%by mass, and the average primary particle size was 183 nm.

The resulting aqueous dispersion of PTFE was diluted with deionizedwater to have a solid concentration of about 10% by mass and coagulatedunder a high-speed stirring condition. The coagulated wet powder wasdried at 150° C. for 18 hours. Various physical properties of theresulting PTFE powder were measured. The results are shown in thetables.

Example 10

Polymerization was performed in the same manner as in Example 9 exceptthat unlike in Example 9, a polymer C (a weight average molecular weightof 20.0×10⁴, a number average molecular weight of 5.8×10⁴, and thecontent of the polymerization unit CH₂═CF(CF₂OCFCF₃COONH₄) being 92.4mol % based on all polymerization units) that is a copolymer of TFE anda monomer represented by CH₂═CF(CF₂OCFCF₃COONH₄) was used in place ofthe polymer B. The solid content of the resulting aqueous dispersion ofPTFE was 19.6% by mass, and the average primary particle size was 350nm. Various physical properties of the resulting PTFE powder weremeasured. The results are shown in the tables.

TABLE 2 Average Solid primary Standard Endothermic concen- particleAspect specific peak Extrusion tration size rate gravity temperatureModifying monomer Modifying monomer pressure % by mass nm — — ° C. Type% by mass Type % by mass MPa Example 1 20.7 218 1.29 2.232 341 HFP 0.054Modifying monomer a 0.006 22.5 Example 2 20.4 227 1.23 2.196 338 PMVE0.016 Modifying monomer a 0.001 26.7 Example 3 26.1 227 1.38 2.168 343HFP 0.029 Modifying monomer a 0.004 23.1 Example 4 20.3 227 1.27 2.203341 HFP 0.040 Modifying monomer a 0.001 24.6 Example 5 23.5 202 1.212.198 340 HFP 0.151 Modifying monomer a 0.005 29.3 Example 6 20.1 2771.60 2.186 343 — — Modifying monomer a 0.006 21.2 Example 1 21.0 1971.88 2.217 336 — — Modifying monomer a 0.011 13.5 Example 8 21.5 2111.33 2.209 340 HFP 0.094 — — — Example 9 21.5 183 1.28 2.174 341 PMVE0.069 — — — Example 10 19.6 350 1.71 2.183 342 PMVE 0.080 — — —

TABLE 3 Polymer A Polymer B Polymer C content content content % by mass% by mass % by mass Example 1 0.38 Example 2 0.39 Example 3 0.43 Example4 0.39 Example 5 0.32 Example 6 0.40 Example 7 0.75 Example 8 0.34Example 9 0.36 Example 10 0.41

Preparation Example 1

To a reactor, 220 g of a monomer D represented by CH₂═CF(CF₂OCFCF₃COOH)and 513 g of water were added, and, moreover, 0.5 mol % of ammoniumpersulfate (APS) based on the monomer D was added. The mixture washeated and stirred at 60° C. for 24 hours in a nitrogen atmosphere toobtain a polymer D aqueous solution D-1 containing the polymer D that isa homopolymer of CH₂═CF(CF₂OCFCF₃COOH). As a result of GPC analysis ofthe resulting polymer D aqueous solution D-1, the polymer D had a Mw of180,000, a Mn of 86,000, and a content of the dimer and the trimer of2.0% by mass based on the polymer D.

Water was added to the resulting polymer D aqueous solution D-1 toadjust the concentration of polymer D to 5.0% by mass, and then theaqueous solution was brought into contact with an ultrafiltrationmembrane (a molecular weight cut-off of 50,000 Da, made of polyethylene)at 30° C. at a water pressure of 0.1 MPa to carry out ultrafiltration.While suitably adding water, ultrafiltration was continued until afiltrate of water in an amount 7 times greater than the aqueous solutionwas eventually eluted, and thus a polymer D aqueous solution D-2 wasobtained. As a result of GPC analysis of the resulting polymer D aqueoussolution D-2, the polymer D had a Mw of 180,000, a Mn of 140,000, and acontent of the dimer and the trimer of less than 1 mass ppm based on thepolymer D. The concentration of the resulting polymer D aqueous solutionD-2 was 5.0% by mass.

Example 11

To a reactor made of SUS with an internal volume of 6 L and equippedwith a stirrer, 3,457 g of deionized water, 180 g of paraffin wax, 107.4g of the polymer D aqueous solution D-2, and 1.1 g of an aqueoussolution of isopropanol having a concentration of 1.0% by mass wereadded. Aqueous ammonia was added to adjust the pH to 9.1. Next, thecontents of the reactor were suctioned while being heated to 70° C.,and, at the same time, the reactor was purged with TFE to remove oxygenin the reactor, and the contents were stirred. After 0.54 g of PMVE wasadded to the reactor, TFE was added until the pressure was 0.73 MPaG.Then, 17.9 mg of an ammonium persulfate (APS) initiator dissolved in 20g of deionized water was added to the reactor such that the pressure ofthe reactor was 0.83 MPaG. After the initiator was added, the pressuredropped, and the initiation of polymerization was observed. TFE wasadded to the reactor to maintain a constant pressure of 0.78 MPaG. WhenTFE consumed in the reaction reached about 180 g, the supply of TFE andstirring were stopped. Subsequently, the gas in the reactor was slowlyreleased until the pressure of the reactor reached 0.02 MPaG.Thereafter, TFE was supplied until the pressure of the reactor was 0.78MPaG, and stirring was started again to continue the reaction. When TFEconsumed in the reaction reached about 540 g, 14.3 mg of hydroquinonedissolved in 20 g of deionized water was added to the reactor, and thereaction was continued. When TFE consumed in the reaction reached about1,200 g, the supply of TFE was stopped, stirring was stopped, and thereaction was terminated. Thereafter, the reactor was evacuated until thepressure in the reactor reached normal pressure, and the contents weretaken out from the reactor and cooled. The supernatant paraffin wax wasremoved from the aqueous dispersion of PTFE. Various physical propertiesof the resulting aqueous dispersion of PTFE were measured. The resultsare shown in the tables.

The resulting aqueous dispersion of PTFE was diluted with deionizedwater to have a solid content of about 10% by mass and coagulated undera high-speed stirring condition. The coagulated wet powder was dried at210° C. for 18 hours. Various physical properties of the resulting PTFEpowder were measured. The results are shown in the tables.

Example 12

Polymerization was performed in the same manner as in Example 11 exceptthat the amount of the aqueous solution of isopropanol added was changedto 2.1 g. Various physical properties of the resulting aqueousdispersion of PTFE were measured. The results are shown in the table.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 13

Polymerization was performed in the same manner as in Example 11 exceptthat the aqueous solution of isopropanol was changed to 1.1 g of anaqueous solution of methanol having a concentration of 1.0% by mass, andthe time to stop the supply of TFE was changed from the time when TFEconsumed in the reaction reached about 1,200 g to the time when TFEconsumed in the reaction reached about 900 g. Various physicalproperties of the resulting aqueous dispersion of PTFE were measured.The results are shown in the table.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 14

Polymerization was performed in the same manner as in Example 11 exceptthat the aqueous solution of isopropanol was changed to 1.8 g of anaqueous solution of Triton X-100 (trade name, manufactured by DowChemical Co., Ltd.) having a concentration of 0.1% by mass (hereinafterreferred to as an aqueous solution of Triton). Various physicalproperties of the resulting aqueous dispersion of PTFE were measured.The results are shown in the table.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 15

Polymerization was performed in the same manner as in Example 11 exceptthat 0.9 g of the aqueous solution of Triton having a concentration of0.1% by mass was further added to the reactor together with the aqueoussolution of isopropanol. Various physical properties of the resultingaqueous dispersion of PTFE were measured. The results are shown in thetable.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 16

Polymerization was performed in the same manner as in Example 11 exceptthat 1.8 g of the aqueous solution of Triton having a concentration of0.1% by mass was further added to the reactor together with the aqueoussolution of isopropanol. Various physical properties of the resultingaqueous dispersion of PTFE were measured. The results are shown in thetable.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 17

Polymerization was performed in the same manner as in Example 11 exceptthat PMVE was changed to 2.4 g of HFP. Various physical properties ofthe resulting aqueous dispersion of PTFE were measured. The results areshown in the table.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 18

Polymerization was performed in the same manner as in Example 11 exceptthat 1.8 g of the aqueous solution of Triton having a concentration of0.1% by mass was further added to the reactor together with the aqueoussolution of isopropanol. Various physical properties of the resultingaqueous dispersion of PTFE were measured. The results are shown in thetable.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 19

Polymerization was performed in the same manner as in Example 15 exceptthat the aqueous solution of Triton added to the reactor was changed to1.25 g of the aqueous solution of Triton having a concentration of 0.1%by mass, the amount of PMVE added was changed to 0.27 g, and a constantpressure was maintained without stopping the feeding of TFE and stirringwhen TFE consumed in the reaction reached about 180 g. Various physicalproperties of the resulting aqueous dispersion of PTFE were measured.The results are shown in the table.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 20

Polymerization was performed in the same manner as in Example 11 exceptthat the aqueous isopropanol solution was not added to the reactor.Various physical properties of the resulting aqueous dispersion of PTFEwere measured. The results are shown in the table.

PTFE powder was obtained in the same manner as in Example 11, andvarious physical properties of the resulting PTFE powder were measured.The results are shown in the table.

TABLE 4 Average Solid primary Standard Endothermic concen- particleAspect specific peak tration size ratio gravity temperature Modifyingmonomer % by mass nm — — ° C. Type % by mass Example 11 25.5 294 1.452.174 341 PMVE 0.035 Example 1 2 24.2 280 1.42 2.180 342 PMVE 0.038Example 13 19.7 328 1.46 2.189 340 PMVE 0.049 Example 14 24.9 331 1.462.158 343 PMVE 0.036 Example 15 24.6 266 1.44 2.174 341 PMVE 0.037Example 16 24.4 215 1.37 2.173 341 PMVE 0.037 Example 17 25.0 310 1.482.177 342 HFP 0.105 Example 18 24.4 261 1.36 2.176 342 HFP 0.094 Example19 24.7 251 1.49 2.175 340 PMVE 0.046 Example 20 24.5 372 1.59 2.159 343PMVE 0.037

TABLE 5 Appear- Stress ance of Extrusion Breaking relaxation stretchedPolymer D pressure strength time body content MPa N sec — % by massExample 11 26.0 21.0 211 Uniform 0.44 Example 12 25.1 20.8 214 Uniform0.47 Example 13 27.5 0.61 Example 14 25.6 20.2 311 Uniform 0.45 Example15 26.4 21.7 221 Uniform 0.46 Example 16 26.3 22.5 253 Uniform 0.46Example 17 25.9 18.1 432 Uniform 0.45 Example 18 25.3 18.6 232 Uniform0.46 Example 19 25.7 20.3 257 Uniform 0.46 Example 20 25.5 17.4 209Uniform 0.46

Preparation Example 2

First, 10 g of a monomer E represented by CF₂═CFOCF₂CF₂COOH, 30 g ofwater, and APS (6.0 mol % based on the monomer E) were added to areactor, and the mixture was heated and stirred at 80° C. for 23 hoursin a nitrogen atmosphere to obtain a polymer E aqueous solution E-1containing the polymer E that is a homopolymer of CF₂═CFOCF₂CF₂COOH. Asa result of GPC analysis of the resulting polymer E aqueous solutionE-1, the polymer E had a Mw of 7,000 and a Mn of 5,000.

Water was added to the resulting polymer E aqueous solution E-1 andbrought into contact with a dialysis membrane (a molecular weightcut-off of 35,000 Da, made of polyethylene) at 30° C. to performfiltration, and thus a polymer E aqueous solution E-2 was obtained. As aresult of GPC analysis of the resulting polymer E aqueous solution E-2,the polymer E had a Mw of 7,000, a Mn of 6,000, and a content of thedimer and the trimer of less than 1 mass ppm based on the polymer E. Theconcentration of the resulting polymer E aqueous solution E-2 was 3.6%by mass.

Example 21

To a reactor made of glass with an internal volume of 1 L and equippedwith a stirrer, 515 g of deionized water, 30 g of paraffin wax, and15.28 g of the polymer E aqueous solution E-2 were added, and aqueousammonia was added to adjust the pH to 9.2. Next, the contents of thereactor were suctioned while being heated to 70° C., and, at the sametime, the reactor was purged with a TFE monomer to remove oxygen in thereactor. Thereafter, the contents were stirred at 540 rpm. After 0.13 gof PMVE was added to the reactor, the TFE monomer was added until thepressure was 0.73 MPaG.

Then, 2.75 mg of an ammonium persulfate (APS) initiator dissolved in 20g of deionized water was added to the reactor such that the pressure ofthe reactor was 0.83 MPaG. After the initiator was added, the pressuredropped, and the initiation of polymerization was observed. The TFEmonomer was added to the reactor to maintain pressure, andpolymerization was continued until about 140 g of the TFE monomerreacted. Thereafter, the reactor was evacuated until the pressure in thereactor reached normal pressure, and the contents were taken out fromthe reactor and cooled. The supernatant paraffin wax was removed fromthe aqueous dispersion of PTFE.

The solid content of the resulting aqueous dispersion of PTFE was 21.0%by mass, and the average primary particle size was 216 nm.

The resulting aqueous dispersion of PTFE was diluted with deionizedwater to have a solid concentration of about 10% by mass and coagulatedunder a high-speed stirring condition. The coagulated wet powder wasdried at 150° C. for 18 hours. Various physical properties of theresulting PTFE powder were measured. The results are shown in the table.

Example 22

Polymerization was performed in the same manner as in Example 21 exceptthat 0.13 g of PMVE was changed to 0.18 g of HFP, and the supply of theTFE monomer was stopped when the amount of the TFE monomer consumed inthe reaction reached about 70 g.

The solid content of the resulting aqueous dispersion of PTFE was 10.7%by mass, and the average primary particle size was 221 nm.

The resulting PTFE aqueous dispersion was diluted with deionized waterto have a solid concentration of about 10% by mass and coagulated undera high-speed stirring condition. The coagulated wet powder was dried at150° C. for 18 hours. Various physical properties of the resulting PTFEpowder were measured. The results are shown in the table.

Preparation Example 3

First, 4.1 g of a monomer F represented by CF₂═CFOCF₂CF(CF₃)OCF₂COOH,5.2 g of CF₂═CF₂, and APS (8.8 mol % based on the monomer F) were addedto a reactor, and the mixture was heated and stirred at 80° C. for 7hours in a nitrogen atmosphere to obtain a polymer F aqueous solutionF-1 containing a copolymer (copolymer F) of a monomer F represented byCF₂═CFOCF₂CF(CF₃)OCF₂COOH and CF₂═CF₂. As a result of GPC analysis ofthe resulting polymer F aqueous solution F-1, the polymer F had a Mw of7,000 and a Mn of 4,000.

The resulting polymer F aqueous solution F-1 was brought into contactwith a dialysis membrane (a molecular weight cut-off of 35,000 Da, madeof polyethylene) at 30° C. to perform filtration, and thus a polymer Faqueous solution F-2 was obtained. As a result of GPC analysis of theresulting polymer F aqueous solution F-2, the polymer F had a Mw of9,000, a Mn of 6,000, and a content of the dimer and the trimer of themonomer F of less than 1 mass ppm based on the polymer F. Theconcentration of the resulting polymer F aqueous solution F-2 was 2.0%by mass.

Example 23

Polymerization was performed in the same manner as in Example 21 exceptthat 515 g of deionized water was changed to 500 g of deionized water,and 15.28 g of the polymer E aqueous solution E-2 was changed to 27.50 gof the polymer F aqueous solution F-2. The solid content of theresulting aqueous dispersion of PTFE was 20.8% by mass, and the averageprimary particle size was 200 nm.

After PTFE powder was obtained in the same manner as in Example 21,various physical properties of the resulting PTFE powder were measured.The results are shown in the table.

Example 24

Polymerization was performed in the same manner as in Example 2 exceptthat 515 g of deionized water was changed to 500 g of deionized water,15.28 g of the polymer E aqueous solution E-2 was changed to 27.50 g ofthe polymer F aqueous solution F-2, 0.13 g of PMVE was changed to 0.18 gof HFP, and the supply of the TFE monomer was stopped when the amount ofthe TFE monomer consumed in the reaction reached about 70 g. The solidcontent of the resulting aqueous dispersion of PTFE was 13.8% by mass,and the average primary particle size was 190 nm.

After PTFE powder was obtained in the same manner as in Example 21,various physical properties of the resulting PTFE powder were measured.The results are shown in the table.

TABLE 6 Example 21 Example 22 Example 23 Example 24 Modifying monomerPMVE HFP PMVE HFP Modifying monomer content % by mass 0.072 0.074 0.0750.081 Aspect ratio — 1.22 1.75 1.29 1.45 Standard specific gravity —2.168 2.205 2.167 2.190 Endothermic peak temperature ° C. 343 341 342340 Polymer E content % by mass 0.35 0.79 Polymer F content % by mass0.36 0.59

1. A method for producing modified polytetrafluoroethylene comprising:polymerizing tetrafluoroethylene and a modifying monomer in an aqueousmedium in the presence of a polymer (I) containing a polymerization unit(I) based on a monomer represented by the following general formula (I)to obtain a modified polytetrafluoroethylene:CX¹X³═CX²R(—CZ¹Z²-A⁰)_(m)  (I) wherein X¹ and X³ are each independentlyF, Cl, H, or CF₃; X² is H, F, an alkyl group, or a fluorine-containingalkyl group; A⁰ is an anionic group; R is a linking group; Z¹ and Z² areeach independently H, F, an alkyl group, or a fluorine-containing alkylgroup; and m is an integer of 1 or more.
 2. The production methodaccording to claim 1, further comprising: adding the modifying monomerbefore the initiation of polymerization or when the concentration ofparticles of the modified polytetrafluoroethylene formed in the aqueousmedium is 5.0% by mass or less.
 3. The production method according toclaim 1, wherein the total amount of the modifying monomer is 0.00001%by mass or more based on the obtained modified polytetrafluoroethylene.4. The production method according to claim 1, wherein the total amountof the modifying monomer is 1.0% by mass or less based on the obtainedmodified polytetrafluoroethylene.
 5. The production method according toclaim 1, wherein the modifying monomer includes at least one selectedfrom the group consisting of hexafluoropropylene, a perfluoro(alkylvinyl ether) and a (perfluoroalkyl)ethylene.
 6. The production methodaccording to claim 1, wherein the modifying monomer is a compoundrepresented by the following general formula (4):CX^(i)X^(k)═CX^(j)R^(a)—(CZ¹Z²)_(k)—Y³  (4) wherein X^(i), X^(j), andX^(k) are each independently F, Cl, H, or CF₃; Y³ is a hydrophilicgroup; R^(a) is a linking group; Z¹ and Z² are each independently H, F,or CF₃; and k is 0 or
 1. 7. The production method according to claim 1,wherein in the polymerization, tetrafluoroethylene and the modifyingmonomer are polymerized further in the presence of a nucleating agent.8. The production method according to claim 7, wherein the nucleatingagent is a nonionic surfactant.
 9. The production method according toclaim 1, wherein the modified polytetrafluoroethylene has an averageprimary particle size of 500 nm or less.
 10. The production methodaccording to claim 1, wherein the modified polytetrafluoroethylene hasan aspect ratio of primary particles of less than 2.00.
 11. Theproduction method according to claim 1, wherein the anionic group is ananionic group that is a sulfate group, a carboxylate group, a phosphategroup, a phosphonate group, a sulfonate group, or —C(CF₃)₂OM wherein Mis —H, a metal atom, —NR⁷ ₄, imidazolium optionally having asubstituent, pyridinium optionally having a substituent, or phosphoniumoptionally having a substituent, and R⁷ is H or an organic group.
 12. Acomposition comprising: a modified polytetrafluoroethylene; and apolymer (I) containing a polymerization unit (I) based on a monomerrepresented by the following general formula (I):CX¹X³═CX²R(—CZ¹Z²-A⁰)_(m)  (I) wherein X¹ and X³ are each independentlyF, Cl, H, or CF₃; X² is H, F, an alkyl group, or a fluorine-containingalkyl group; A⁰ is an anionic group; R is a linking group; Z¹ and Z² areeach independently H, F, an alkyl group, or a fluorine-containing alkylgroup; and m is an integer of 1 or more.
 13. The composition accordingto claim 12, having a breaking strength of 10.0 N or more.
 14. Thecomposition according to claim 12, having a stress relaxation time of 50seconds or more.
 15. The composition according to claim 12, having anextrusion pressure of 10.0 MPa or more and 30.0 MPa or less.
 16. Thecomposition according to claim 12, having an endothermic peaktemperature in the range of 333 to 347° C.
 17. The composition accordingto claim 12, having a standard specific gravity of 2.250 or less. 18.The composition according to claim 12, wherein the modifiedpolytetrafluoroethylene has an aspect ratio of primary particles of lessthan 2.00.
 19. The composition according to claim 12, wherein theanionic group is an anionic group that is a sulfate group, a carboxylategroup, a phosphate group, a phosphonate group, a sulfonate group, or—C(CF₃)₂OM wherein M is —H, a metal atom, —NR⁷ ₄, imidazolium optionallyhaving a substituent, pyridinium optionally having a substituent, orphosphonium optionally having a substituent, and R⁷ is H or an organicgroup.
 20. The composition according to claim 12, which is substantiallyfree from a fluorine-containing surfactant.
 21. The compositionaccording to claim 12, which is a powder.